diff --git a/clang/cmake/caches/Release.cmake b/clang/cmake/caches/Release.cmake
index 23e99493087ff..a1c68fc51dbd0 100644
--- a/clang/cmake/caches/Release.cmake
+++ b/clang/cmake/caches/Release.cmake
@@ -48,10 +48,8 @@ set(CLANG_ENABLE_BOOTSTRAP ON CACHE BOOL "")
 
 set(STAGE1_PROJECTS "clang")
 
-# Building Flang on Windows requires compiler-rt, so we need to build it in
-# stage1.  compiler-rt is also required for building the Flang tests on
-# macOS.
-set(STAGE1_RUNTIMES "compiler-rt")
+# Build all runtimes so we can statically link them into the stage2 compiler.
+set(STAGE1_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind")
 
 if (LLVM_RELEASE_ENABLE_PGO)
   list(APPEND STAGE1_PROJECTS "lld")
@@ -90,9 +88,20 @@ else()
   set(CLANG_BOOTSTRAP_TARGETS ${LLVM_RELEASE_FINAL_STAGE_TARGETS} CACHE STRING "")
 endif()
 
+if (LLVM_RELEASE_ENABLE_LTO)
+  # Enable LTO for the runtimes.  We need to configure stage1 clang to default
+  # to using lld as the linker because the stage1 toolchain will be used to
+  # build and link the runtimes.
+  # FIXME: We can't use LLVM_ENABLE_LTO=Thin here, because it causes the CMake
+  # step for the libcxx build to fail.  CMAKE_INTERPROCEDURAL_OPTIMIZATION does
+  # enable ThinLTO, though.
+  set(RUNTIMES_CMAKE_ARGS "-DCMAKE_INTERPROCEDURAL_OPTIMIZATION=ON -DLLVM_ENABLE_LLD=ON" CACHE STRING "")
+endif()
+
 # Stage 1 Common Config
 set(LLVM_ENABLE_RUNTIMES ${STAGE1_RUNTIMES} CACHE STRING "")
 set(LLVM_ENABLE_PROJECTS ${STAGE1_PROJECTS} CACHE STRING "")
+set(LIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY ON CACHE STRING "")
 
 # stage2-instrumented and Final Stage Config:
 # Options that need to be set in both the instrumented stage (if we are doing
@@ -102,6 +111,16 @@ set_instrument_and_final_stage_var(LLVM_ENABLE_LTO "${LLVM_RELEASE_ENABLE_LTO}"
 if (LLVM_RELEASE_ENABLE_LTO)
   set_instrument_and_final_stage_var(LLVM_ENABLE_LLD "ON" BOOL)
 endif()
+set_instrument_and_final_stage_var(LLVM_ENABLE_LIBCXX "ON" BOOL)
+set_instrument_and_final_stage_var(LLVM_STATIC_LINK_CXX_STDLIB "ON" BOOL)
+set(RELEASE_LINKER_FLAGS "-rtlib=compiler-rt --unwindlib=libunwind")
+if(NOT ${CMAKE_HOST_SYSTEM_NAME} MATCHES "Darwin")
+  set(RELEASE_LINKER_FLAGS "${RELEASE_LINKER_FLAGS} -static-libgcc")
+endif()
+
+set_instrument_and_final_stage_var(CMAKE_EXE_LINKER_FLAGS ${RELEASE_LINKER_FLAGS} STRING)
+set_instrument_and_final_stage_var(CMAKE_SHARED_LINKER_FLAGS ${RELEASE_LINKER_FLAGS} STRING)
+set_instrument_and_final_stage_var(CMAKE_MODULE_LINKER_FLAGS ${RELEASE_LINKER_FLAGS} STRING)
 
 # Final Stage Config (stage2)
 set_final_stage_var(LLVM_ENABLE_RUNTIMES "${LLVM_RELEASE_ENABLE_RUNTIMES}" STRING)