Index: libcxx/test/configs/llvm-libc++-mingw.cfg.in
===================================================================
--- libcxx/test/configs/llvm-libc++-mingw.cfg.in
+++ libcxx/test/configs/llvm-libc++-mingw.cfg.in
@@ -11,7 +11,7 @@
     '-nostdlib++ -L %{lib} -lc++'
 ))
 config.substitutions.append(('%{exec}',
-    '%{executor} --execdir %T --env PATH=%{lib} -- '
+    '%{executor} --execdir %T --prepend_env PATH=%{lib} -- '
 ))
 
 import os, site
Index: libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in
===================================================================
--- libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in
+++ libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in
@@ -11,7 +11,7 @@
     '-nostdlib -L %{lib} -lc++ -lmsvcrt -lmsvcprt -loldnames'
 ))
 config.substitutions.append(('%{exec}',
-    '%{executor} --execdir %T --env PATH=%{lib} -- '
+    '%{executor} --execdir %T --prepend_env PATH=%{lib} -- '
 ))
 
 import os, site
Index: libcxx/test/configs/llvm-libc++-shared-no-vcruntime-clangcl.cfg.in
===================================================================
--- libcxx/test/configs/llvm-libc++-shared-no-vcruntime-clangcl.cfg.in
+++ libcxx/test/configs/llvm-libc++-shared-no-vcruntime-clangcl.cfg.in
@@ -12,7 +12,7 @@
     '-nostdlib -L %{lib} -lc++ -lmsvcrt -lmsvcprt -loldnames'
 ))
 config.substitutions.append(('%{exec}',
-    '%{executor} --execdir %T --env PATH=%{lib} -- '
+    '%{executor} --execdir %T --prepend_env PATH=%{lib} -- '
 ))
 
 import os, site
Index: libcxx/utils/ci/buildkite-pipeline.yml
===================================================================
--- libcxx/utils/ci/buildkite-pipeline.yml
+++ libcxx/utils/ci/buildkite-pipeline.yml
@@ -31,678 +31,6 @@
   # Light pre-commit tests for things like formatting or when people forget
   # to update generated files.
   #
-  - label: "Format"
-    command: "libcxx/utils/ci/run-buildbot check-format"
-    artifact_paths:
-      - "**/clang-format.patch"
-    env:
-        GIT_CLANG_FORMAT: "/usr/bin/git-clang-format-${LLVM_STABLE_VERSION} --binary clang-format-${LLVM_STABLE_VERSION}"
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "Generated output"
-    command: "libcxx/utils/ci/run-buildbot check-generated-output"
-    artifact_paths:
-      - "**/generated_output.patch"
-      - "**/generated_output.status"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        CLANG_FORMAT: "/usr/bin/clang-format-${LLVM_STABLE_VERSION}"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "Documentation"
-    command: "libcxx/utils/ci/run-buildbot documentation"
-    artifact_paths:
-      - "**/test-results.xml"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  #
-  # General testing with the default configuration, under all the supported
-  # Standard modes, with Clang and GCC. This catches most issues upfront.
-  # The goal of this step is to catch most issues while being very fast.
-  #
-  - wait
-
-  - label: "GCC ${GCC_STABLE_VERSION} / C++latest"
-    command: "libcxx/utils/ci/run-buildbot generic-gcc"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "gcc-${GCC_STABLE_VERSION}"
-        CXX: "g++-${GCC_STABLE_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "C++2b"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx2b"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "Modular build"
-    command: "libcxx/utils/ci/run-buildbot generic-modules"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "C++11"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx11"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "C++03"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx03"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  #
-  # All other supported configurations of libc++.
-  #
-  - wait
-
-  - label: "C++20"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx20"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "C++17"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx17"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "C++14"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx14"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  # Tests with the supported compilers.
-  - label: "GCC ${GCC_STABLE_VERSION} / C++11"
-    command: "libcxx/utils/ci/run-buildbot generic-gcc-cxx11"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "gcc-${GCC_STABLE_VERSION}"
-        CXX: "g++-${GCC_STABLE_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "Clang 15"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx2b"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-15"
-        CXX: "clang++-15"
-        # TODO LLVM18: Enable clang-tidy
-        # ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "Clang 16"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx2b"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-16"
-        CXX: "clang++-16"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  # Tests with the sanitizers.
-  - group: "Sanitizers"
-    steps:
-    - label: "ASAN"
-      command: "libcxx/utils/ci/run-buildbot generic-asan"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "TSAN"
-      command: "libcxx/utils/ci/run-buildbot generic-tsan"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "UBSAN"
-      command: "libcxx/utils/ci/run-buildbot generic-ubsan"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "MSAN"
-      command: "libcxx/utils/ci/run-buildbot generic-msan"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-  # Tests with the various supported ways to build libc++.
-  - label: "Bootstrapping build"
-    command: "libcxx/utils/ci/run-buildbot bootstrapping-build"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-      - "**/crash_diagnostics/*"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        LLVM_SYMBOLIZER_PATH: "/usr/bin/llvm-symbolizer-${LLVM_HEAD_VERSION}"
-        CLANG_CRASH_DIAGNOSTICS_DIR: "crash_diagnostics"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  # Tests with various build configurations.
-  - label: "Static libraries"
-    command: "libcxx/utils/ci/run-buildbot generic-static"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "Shared library with merged ABI and unwinder libraries"
-    command: "libcxx/utils/ci/run-buildbot generic-merged"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "Assertions enabled"
-    command: "libcxx/utils/ci/run-buildbot generic-assertions"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "Debug mode"
-    command: "libcxx/utils/ci/run-buildbot generic-debug-mode"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "With LLVM's libunwind"
-    command: "libcxx/utils/ci/run-buildbot generic-with_llvm_unwinder"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - label: "Modular build with Local Submodule Visibility"
-    command: "libcxx/utils/ci/run-buildbot generic-modules-lsv"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  - group: "Parts disabled"
-    steps:
-    - label: "No threads"
-      command: "libcxx/utils/ci/run-buildbot generic-no-threads"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "No filesystem"
-      command: "libcxx/utils/ci/run-buildbot generic-no-filesystem"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "No random device"
-      command: "libcxx/utils/ci/run-buildbot generic-no-random_device"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "No fstream"
-      command: "libcxx/utils/ci/run-buildbot generic-no-fstream"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "No locale"
-      command: "libcxx/utils/ci/run-buildbot generic-no-localization"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "No Unicode"
-      command: "libcxx/utils/ci/run-buildbot generic-no-unicode"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "No wide characters"
-      command: "libcxx/utils/ci/run-buildbot generic-no-wide-characters"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "No experimental features"
-      command: "libcxx/utils/ci/run-buildbot generic-no-experimental"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "No exceptions"
-      command: "libcxx/utils/ci/run-buildbot generic-noexceptions"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang-${LLVM_HEAD_VERSION}"
-          CXX: "clang++-${LLVM_HEAD_VERSION}"
-          ENABLE_CLANG_TIDY: "On"
-      agents:
-        queue: "libcxx-builders"
-        os: "linux"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-  - label: "Unstable ABI"
-    command: "libcxx/utils/ci/run-buildbot generic-abi-unstable"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  # Other non-testing CI jobs
-  - label: "Benchmarks"
-    command: "libcxx/utils/ci/run-buildbot benchmarks"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    env:
-        CC: "clang-${LLVM_HEAD_VERSION}"
-        CXX: "clang++-${LLVM_HEAD_VERSION}"
-        ENABLE_CLANG_TIDY: "On"
-    agents:
-      queue: "libcxx-builders"
-      os: "linux"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    timeout_in_minutes: 120
-
-  # Tests on non-Unix platforms
-  - group: ":windows: Windows"
-    steps:
     - label: "Clang-cl (DLL)"
       command: "bash libcxx/utils/ci/run-buildbot clang-cl-dll"
       artifact_paths:
@@ -779,268 +107,3 @@
           - exit_status: -1  # Agent was lost
             limit: 2
       timeout_in_minutes: 120
-
-  - group: ":apple: Apple"
-    steps:
-    - label: "MacOS x86_64"
-      command: "libcxx/utils/ci/run-buildbot generic-cxx20"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders"
-        os: "macos"
-        arch: "x86_64"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "MacOS arm64"
-      command: "libcxx/utils/ci/run-buildbot generic-cxx20"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders"
-        os: "macos"
-        arch: "arm64"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "MacOS with Modules"
-      command: "libcxx/utils/ci/run-buildbot generic-modules"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders"
-        os: "macos"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    # Build with the configuration we use to generate libc++.dylib on Apple platforms
-    - label: "Apple system"
-      command: "libcxx/utils/ci/run-buildbot apple-system"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders"
-        os: "macos"
-        arch: "arm64" # This can technically run on any architecture, but we have more resources on arm64 so we pin this job to arm64
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    # Test back-deployment to older Apple platforms
-    - label: "Apple back-deployment macosx10.9"
-      command: "libcxx/utils/ci/run-buildbot apple-system-backdeployment-10.9"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders"
-        os: "macos"
-        arch: "x86_64" # We need to use x86_64 for back-deployment CI on this target since macOS didn't support arm64 back then.
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "Apple back-deployment macosx10.15"
-      command: "libcxx/utils/ci/run-buildbot apple-system-backdeployment-10.15"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders"
-        os: "macos"
-        arch: "x86_64" # We need to use x86_64 for back-deployment CI on this target since macOS didn't support arm64 back then.
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "Apple back-deployment macosx11.0 arm64"
-      command: "libcxx/utils/ci/run-buildbot apple-system-backdeployment-11.0"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders"
-        os: "macos"
-        arch: "arm64"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "Apple back-deployment with assertions enabled"
-      command: "libcxx/utils/ci/run-buildbot apple-system-backdeployment-assertions-11.0"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders"
-        os: "macos"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-  - group: "ARM"
-    steps:
-    - label: "AArch64"
-      command: "libcxx/utils/ci/run-buildbot aarch64"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders-linaro-arm"
-        arch: "aarch64"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "AArch64 -fno-exceptions"
-      command: "libcxx/utils/ci/run-buildbot aarch64-noexceptions"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders-linaro-arm"
-        arch: "aarch64"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "Armv8"
-      command: "libcxx/utils/ci/run-buildbot armv8"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders-linaro-arm"
-        arch: "armv8l"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "Armv8 -fno-exceptions"
-      command: "libcxx/utils/ci/run-buildbot armv8-noexceptions"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders-linaro-arm"
-        arch: "armv8l"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "Armv7"
-      command: "libcxx/utils/ci/run-buildbot armv7"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders-linaro-arm"
-        arch: "armv8l" # Compiling for v7, running on v8 hardware
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "Armv7 -fno-exceptions"
-      command: "libcxx/utils/ci/run-buildbot armv7-noexceptions"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      agents:
-        queue: "libcxx-builders-linaro-arm"
-        arch: "armv8l" # Compiling for v7, running on v8 hardware
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-  - group: "AIX"
-    steps:
-    - label: "AIX (32-bit)"
-      command: "libcxx/utils/ci/run-buildbot aix"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang"
-          CXX: "clang++"
-          OBJECT_MODE: "32"
-      agents:
-          queue: libcxx-builders
-          os: aix
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-    - label: "AIX (64-bit)"
-      command: "libcxx/utils/ci/run-buildbot aix"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang"
-          CXX: "clang++"
-          OBJECT_MODE: "64"
-      agents:
-          queue: libcxx-builders
-          os: aix
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
-
-  - group: "FreeBSD"
-    steps:
-    - label: "FreeBSD 13 amd64"
-      command: "libcxx/utils/ci/run-buildbot generic-cxx2b"
-      artifact_paths:
-        - "**/test-results.xml"
-        - "**/*.abilist"
-      env:
-          CC: "clang15"
-          CXX: "clang++15"
-      agents:
-        queue: "libcxx-builders"
-        os: "freebsd"
-      retry:
-        automatic:
-          - exit_status: -1  # Agent was lost
-            limit: 2
-      timeout_in_minutes: 120
Index: libcxx/utils/run.py
===================================================================
--- libcxx/utils/run.py
+++ libcxx/utils/run.py
@@ -24,6 +24,7 @@
     parser.add_argument('--execdir', type=str, required=True)
     parser.add_argument('--codesign_identity', type=str, required=False, default=None)
     parser.add_argument('--env', type=str, nargs='*', required=False, default=dict())
+    parser.add_argument('--prepend_env', type=str, nargs='*', required=False, default=dict())
     parser.add_argument("command", nargs=argparse.ONE_OR_MORE)
     args = parser.parse_args()
     commandLine = args.command
@@ -43,6 +44,14 @@
 
     # Extract environment variables into a dictionary
     env = {k : v  for (k, v) in map(lambda s: s.split('=', 1), args.env)}
+
+    # Set environment variables where we prepend the given value to the
+    # existing environment variable.
+    for (k, v) in map(lambda s: s.split('=', 1), args.prepend_env):
+        if k in os.environ:
+            v = v + os.pathsep + os.environ[k]
+        env[k] = v
+
     if platform.system() == 'Windows':
         # Pass some extra variables through on Windows:
         # COMSPEC is needed for running subprocesses via std::system().