diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -518,6 +518,9 @@
 
 # Required flags ==============================================================
 function(cxx_add_basic_build_flags target)
+  # TODO: Remove this as soon as the false positives in https://reviews.llvm.org/D100581
+  #       have been fixed. This is a gentleman's workaround to avoid reverting D100581.
+  target_add_compile_flags_if_supported(${target} PRIVATE -Wno-unused-but-set-variable)
 
   # Require C++20 for all targets. C++17 is needed to use aligned allocation
   # in the dylib. C++20 is needed to use char8_t.
diff --git a/libcxx/utils/ci/buildkite-pipeline.yml b/libcxx/utils/ci/buildkite-pipeline.yml
--- a/libcxx/utils/ci/buildkite-pipeline.yml
+++ b/libcxx/utils/ci/buildkite-pipeline.yml
@@ -18,41 +18,6 @@
 #
 
 steps:
-  #
-  # 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"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    soft_fail:
-        - exit_status: 1
-
-  - label: "Generated output"
-    command: "libcxx/utils/ci/run-buildbot check-generated-output"
-    artifact_paths:
-      - "**/generated_output.patch"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  #
-  # 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: "C++2b"
     command: "libcxx/utils/ci/run-buildbot generic-cxx2b"
     artifact_paths:
@@ -65,282 +30,6 @@
         - exit_status: -1  # Agent was lost
           limit: 2
 
-  - label: "C++20"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx20"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++17"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx17"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++14"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx14"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-  - label: "C++11"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx11"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "C++03"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx03"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "GCC/C++20"
-    command: "libcxx/utils/ci/run-buildbot generic-gcc"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "GCC-next/C++20"
-    command: "libcxx/utils/ci/run-buildbot generic-gcc-next"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-    soft_fail:
-      - exit_status: 1
-
-  #
-  # All other supported configurations of libc++.
-  #
-  - wait
-
-  - label: "-fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot generic-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Static libraries"
-    command: "libcxx/utils/ci/run-buildbot generic-static"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Debug iterators"
-    command: "libcxx/utils/ci/run-buildbot generic-debug-iterators"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "ASAN"
-    command: "libcxx/utils/ci/run-buildbot generic-asan"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "TSAN"
-    command: "libcxx/utils/ci/run-buildbot generic-tsan"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "UBSAN"
-    command: "libcxx/utils/ci/run-buildbot generic-ubsan"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "With LLVM's libunwind"
-    command: "libcxx/utils/ci/run-buildbot generic-with_llvm_unwinder"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Single-threaded"
-    command: "libcxx/utils/ci/run-buildbot generic-singlethreaded"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No debug mode"
-    command: "libcxx/utils/ci/run-buildbot generic-no-debug"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No Filesystem"
-    command: "libcxx/utils/ci/run-buildbot generic-no-filesystem"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No random device"
-    command: "libcxx/utils/ci/run-buildbot generic-no-random_device"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "No locale"
-    command: "libcxx/utils/ci/run-buildbot generic-no-localization"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Benchmarks"
-    command: "libcxx/utils/ci/run-buildbot benchmarks"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Documentation"
-    command: "libcxx/utils/ci/run-buildbot documentation"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Legacy Lit configuration"
-    command: "libcxx/utils/ci/run-buildbot legacy-test-config"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Legacy standalone build"
-    command: "libcxx/utils/ci/run-buildbot legacy-standalone"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Unified standalone build"
-    command: "libcxx/utils/ci/run-buildbot unified-standalone"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
   - label: "Runtimes build"
     command: "libcxx/utils/ci/run-buildbot runtimes-build"
     artifact_paths:
@@ -351,166 +40,3 @@
       automatic:
         - exit_status: -1  # Agent was lost
           limit: 2
-
-  - label: "Windows (DLL)"
-    command: "bash libcxx/utils/ci/run-buildbot windows-dll"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "windows"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Windows (Static)"
-    command: "bash libcxx/utils/ci/run-buildbot windows-static"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "windows"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "32 bit"
-    command: "libcxx/utils/ci/run-buildbot generic-32bit"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "MacOS C++20"
-    command: "libcxx/utils/ci/run-buildbot generic-cxx20"
-    artifact_paths:
-      - "**/test-results.xml"
-      - "**/*.abilist"
-    agents:
-      queue: "libcxx-builders-macos"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  # Build with the configuration we use to generate libc++.dylib on Apple platforms
-  - label: "Apple system"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Apple system -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  # Test back-deployment to older Apple platforms
-  - label: "Apple back-deployment macosx10.9"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system-backdeployment-10.9"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos10.15" # TODO: For now, we're running the back-deployment tests for 10.9 on 10.15, because we don't have proper 10.9 machines
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Apple back-deployment macosx10.15"
-    command: "libcxx/utils/ci/run-buildbot x86_64-apple-system-backdeployment-10.15"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-macos10.15"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "AArch64"
-    command: "libcxx/utils/ci/run-buildbot aarch64"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "aarch64"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "AArch64 -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot aarch64-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "aarch64"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Armv8"
-    command: "libcxx/utils/ci/run-buildbot armv8"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "armv8l"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Armv8 -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot armv8-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    agents:
-      queue: "libcxx-builders-linaro-arm"
-      arch: "armv8l"
-    retry:
-      automatic:
-        - exit_status: -1  # Agent was lost
-          limit: 2
-
-  - label: "Armv7"
-    command: "libcxx/utils/ci/run-buildbot armv7"
-    artifact_paths:
-      - "**/test-results.xml"
-    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
-
-  - label: "Armv7 -fno-exceptions"
-    command: "libcxx/utils/ci/run-buildbot armv7-noexceptions"
-    artifact_paths:
-      - "**/test-results.xml"
-    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
diff --git a/libcxx/utils/libcxx/test/params.py b/libcxx/utils/libcxx/test/params.py
--- a/libcxx/utils/libcxx/test/params.py
+++ b/libcxx/utils/libcxx/test/params.py
@@ -24,6 +24,10 @@
   '-Wno-aligned-allocation-unavailable',
   '-Wno-atomic-alignment',
 
+  # TODO: Remove this as soon as the false positives in https://reviews.llvm.org/D100581
+  #       have been fixed. This is a gentleman's workaround to avoid reverting D100581.
+  '-Wno-unused-but-set-variable',
+
   # GCC warns about places where we might want to add sized allocation/deallocation
   # functions, but we know better what we're doing/testing in the test suite.
   '-Wno-sized-deallocation',