[CMake][Release] Statically link clang with stage1 runtimes (#127268)

This change will cause clang and the other tools to statically link
against the runtimes built in stage1. This will make the built binaries
more portable by eliminating dependencies on system libraries like
libgcc and libstdc++.

(cherry picked from commit f5b311e)

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)