[clang] [CMake] Add a cache file for building a highly-optimized LLVM toolchain (PR #117802)

[Tom Stellard via cfe-commits]

================
@@ -0,0 +1,17 @@
+# Stage 1
+# * Build an LTO optimized libcxx, so we can staticially link it into stage 2
+#   clang.
+
+
+set(CMAKE_BUILD_TYPE Release CACHE STRING "")
+set(LLVM_TARGETS_TO_BUILD Native CACHE STRING "")
+set(LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind" CACHE STRING "" FORCE)
+set(LLVM_ENABLE_PROJECTS "clang;lld" CACHE STRING "" FORCE)
+
+set(CLANG_ENABLE_BOOTSTRAP ON CACHE BOOL "")
+set(CLANG_BOOTSTRAP_CMAKE_ARGS -C ${CMAKE_CURRENT_LIST_DIR}/stage2-instrumented.cmake CACHE BOOL "")
+set(BOOTSTRAP_LLVM_BUILD_INSTRUMENTED IR CACHE BOOL "")
----------------
tstellar wrote:

No, it's not.  This needs to be set in the stage1 config: https://github.com/llvm/llvm-project/blob/main/clang/CMakeLists.txt#L597

https://github.com/llvm/llvm-project/pull/117802