diff --git a/compiler-rt/cmake/Modules/AddCompilerRT.cmake b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
--- a/compiler-rt/cmake/Modules/AddCompilerRT.cmake
+++ b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
@@ -565,13 +565,9 @@
                       -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER})
   endif()
 
-  set(STAMP_DIR ${prefix}-stamps/)
-  set(BINARY_DIR ${prefix}-bins/)
-
   add_custom_target(${name}-clear
-    COMMAND ${CMAKE_COMMAND} -E remove_directory ${BINARY_DIR}
-    COMMAND ${CMAKE_COMMAND} -E remove_directory ${STAMP_DIR}
-    COMMENT "Clobbering ${name} build and stamp directories"
+    COMMAND ${CMAKE_COMMAND} -E remove_directory ${prefix}
+    COMMENT "Clobbering ${name} build directories"
     USES_TERMINAL
     )
   set_target_properties(${name}-clear PROPERTIES FOLDER "Compiler-RT Misc")
@@ -579,10 +575,9 @@
   add_custom_command(
     OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${name}-clobber-stamp
     DEPENDS ${LIBCXX_DEPS} ${toolchain_deps}
-    COMMAND ${CMAKE_COMMAND} -E touch ${BINARY_DIR}/CMakeCache.txt
-    COMMAND ${CMAKE_COMMAND} -E touch ${STAMP_DIR}/${name}-mkdir
+    COMMAND ${CMAKE_COMMAND} -E touch ${prefix}/CMakeCache.txt
     COMMAND ${CMAKE_COMMAND} -E touch ${CMAKE_CURRENT_BINARY_DIR}/${name}-clobber-stamp
-    COMMENT "Clobbering bootstrap build and stamp directories"
+    COMMENT "Clobbering bootstrap build directories"
     )
 
   add_custom_target(${name}-clobber
@@ -629,10 +624,9 @@
 
   ExternalProject_Add(${name}
     DEPENDS ${name}-clobber ${LIBCXX_DEPS}
-    PREFIX ${prefix}
-    SOURCE_DIR ${COMPILER_RT_SOURCE_DIR}/cmake/Modules/CustomLibcxx
-    STAMP_DIR ${STAMP_DIR}
-    BINARY_DIR ${BINARY_DIR}
+    PREFIX ${CMAKE_CURRENT_BINARY_DIR}/${name}
+    SOURCE_DIR ${LLVM_MAIN_SRC_DIR}/../runtimes
+    BINARY_DIR ${prefix}
     CMAKE_ARGS ${CMAKE_PASSTHROUGH_VARIABLES}
                ${compiler_args}
                -DCMAKE_C_FLAGS=${LIBCXX_C_FLAGS}
@@ -640,10 +634,19 @@
                -DCMAKE_BUILD_TYPE=Release
                -DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY
                -DLLVM_PATH=${LLVM_MAIN_SRC_DIR}
-               -DLLVM_BINARY_DIR=${prefix}
-               -DLLVM_LIBRARY_OUTPUT_INTDIR=${prefix}/lib
-               -DCOMPILER_RT_LIBCXX_PATH=${COMPILER_RT_LIBCXX_PATH}
-               -DCOMPILER_RT_LIBCXXABI_PATH=${COMPILER_RT_LIBCXXABI_PATH}
+               -DLLVM_ENABLE_RUNTIMES=libcxx|libcxxabi
+               -DLIBCXXABI_ENABLE_SHARED=OFF
+               -DLIBCXXABI_ENABLE_EXCEPTIONS=OFF
+               -DLIBCXXABI_HERMETIC_STATIC_LIBRARY=ON
+               -DLIBCXXABI_INCLUDE_TESTS=OFF
+               -DLIBCXX_ENABLE_EXPERIMENTAL_LIBRARY=OFF
+               -DLIBCXX_ENABLE_SHARED=OFF
+               -DLIBCXX_ENABLE_EXCEPTIONS=OFF
+               -DLIBCXX_HERMETIC_STATIC_LIBRARY=ON
+               -DLIBCXX_INCLUDE_TESTS=OFF
+               -DLIBCXX_CXX_ABI=libcxxabi
+               -DLIBCXX_CXX_ABI_INTREE=1
+               -DLIBCXX_ENABLE_STATIC_ABI_LIBRARY=ON
                ${LIBCXX_CMAKE_ARGS}
     INSTALL_COMMAND ""
     STEP_TARGETS configure build
@@ -651,14 +654,14 @@
     USES_TERMINAL_CONFIGURE 1
     USES_TERMINAL_BUILD 1
     USES_TERMINAL_INSTALL 1
+    LIST_SEPARATOR |
     EXCLUDE_FROM_ALL TRUE
-    BUILD_BYPRODUCTS "${prefix}/lib/libc++.a" "${prefix}/lib/libc++abi.a"
     )
 
   if (CMAKE_GENERATOR MATCHES "Make")
-    set(run_clean "$(MAKE)" "-C" "${BINARY_DIR}" "clean")
+    set(run_clean "$(MAKE)" "-C" "${prefix}" "clean")
   else()
-    set(run_clean ${CMAKE_COMMAND} --build ${BINARY_DIR} --target clean
+    set(run_clean ${CMAKE_COMMAND} --build ${prefix} --target clean
                                    --config "$<CONFIG>")
   endif()
 
@@ -667,7 +670,7 @@
     COMMENT "Cleaning ${name}..."
     DEPENDEES configure
     ${force_deps}
-    WORKING_DIRECTORY ${BINARY_DIR}
+    WORKING_DIRECTORY ${prefix}
     EXCLUDE_FROM_MAIN 1
     USES_TERMINAL 1
     )
diff --git a/compiler-rt/cmake/Modules/CustomLibcxx/CMakeLists.txt b/compiler-rt/cmake/Modules/CustomLibcxx/CMakeLists.txt
deleted file mode 100644
--- a/compiler-rt/cmake/Modules/CustomLibcxx/CMakeLists.txt
+++ /dev/null
@@ -1,29 +0,0 @@
-# TODO(phosek): We should use the runtimes build instead configured with
-# LLVM_ENABLE_RUNTIMES=libcxxabi;libcxx to avoid duplication of logic.
-
-cmake_minimum_required(VERSION 3.13.4)
-project(custom-libcxx C CXX)
-
-find_package(Python3 REQUIRED COMPONENTS Interpreter)
-
-# Build static libcxxabi.
-set(LIBCXXABI_ENABLE_SHARED OFF CACHE BOOL "")
-set(LIBCXXABI_ENABLE_EXCEPTIONS ON CACHE BOOL "")
-set(LIBCXXABI_HERMETIC_STATIC_LIBRARY ON CACHE STRING "")
-set(LIBCXXABI_LIBCXX_PATH ${COMPILER_RT_LIBCXX_PATH} CACHE PATH "")
-set(LIBCXXABI_INCLUDE_TESTS OFF CACHE BOOL "")
-add_subdirectory(${COMPILER_RT_LIBCXXABI_PATH} ${CMAKE_CURRENT_BINARY_DIR}/cxxabi)
-
-# Build static libcxx without exceptions.
-set(LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY OFF CACHE BOOL "")
-set(LIBCXX_ENABLE_SHARED OFF CACHE BOOL "")
-set(LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
-set(LIBCXX_HERMETIC_STATIC_LIBRARY ON CACHE BOOL "")
-
-# Use above libcxxabi.
-set(LIBCXX_CXX_ABI "libcxxabi" CACHE STRING "")
-set(LIBCXX_CXX_ABI_INTREE 1)
-set(LIBCXX_ENABLE_STATIC_ABI_LIBRARY ON CACHE BOOL "")
-set(LIBCXX_CXX_ABI_INCLUDE_PATHS ${COMPILER_RT_LIBCXXABI_PATH}/include CACHE PATH "")
-
-add_subdirectory(${COMPILER_RT_LIBCXX_PATH} ${CMAKE_CURRENT_BINARY_DIR}/cxx)