This enables multi-stage PGO build optimized by BOLT using BOLT.cmake cache.
The issue is that `-DPGO_BUILD_CONFIGURATION` cache file is passed to both
stage2-instrumented and stage2-optimized builds (for them to be identical),
but in case of BOLT.cmake, it doesn't make sense to BOLT-instrument the
instrumented binary (it's not going to be optimized). Hence turn off
`CLANG_BOLT_INSTRUMENT` code if `LLVM_BUILD_INSTRUMENTED` is enabled.
The final workflow that enables multi-stage InstrPGO+ThinLTO+BOLT Clang build:
```
cmake <llvm-project>/llvm -GNinja -DLLVM_ENABLE_LLD=ON \
-DBOOTSTRAP_LLVM_ENABLE_LLD=ON -DBOOTSTRAP_BOOTSTRAP_LLVM_ENABLE_LLD=ON \
-DPGO_INSTRUMENT_LTO=Thin -C llvm-project/clang/cmake/caches/BOLT-PGO.cmake
ninja stage2-clang++-bolt
```
Reviewed By: rafauler
Differential Revision: https://reviews.llvm.org/D136023
endforeach()
endif()
-if (CLANG_BOLT_INSTRUMENT)
+if (CLANG_BOLT_INSTRUMENT AND NOT LLVM_BUILD_INSTRUMENTED)
set(CLANG_PATH ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang)
set(CLANGXX_PATH ${CLANG_PATH}++)
set(CLANG_INSTRUMENTED ${CLANG_PATH}-bolt.inst)
--- /dev/null
+set(LLVM_ENABLE_PROJECTS "bolt;clang;lld" CACHE STRING "")
+
+set(CLANG_BOOTSTRAP_TARGETS
+ stage2-clang++-bolt
+ CACHE STRING "")
+set(BOOTSTRAP_CLANG_BOOTSTRAP_TARGETS
+ clang++-bolt
+ CACHE STRING "")
+
+set(PGO_BUILD_CONFIGURATION ${CMAKE_CURRENT_LIST_DIR}/BOLT.cmake CACHE STRING "")
+include(${CMAKE_CURRENT_LIST_DIR}/PGO.cmake)