Revert "[Clang][CMake] Use IRPGO instead of FE PGO for Cmake Caches (#155957)" (#159367)

This reverts commit 7fca1f8.

PR #55957 breaks the BOLT buildbot bolt-aarch64-ubuntu-clang:
https://lab.llvm.org/staging/#/builders/126

Example build:
https://lab.llvm.org/staging/#/builders/126/builds/2628

> ld.lld:
/home/buildbot/workspace/bolt-aarch64-ubuntu-clang/llvm-project/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:10194:
bool llvm::LoopVectorizePass::processLoop(llvm::Loop*): Assertion
`!verifyFunction(*F, &dbgs())' failed.

Author: paschalis-mpeis

clang/cmake/caches/PGO.cmake

@@ -5,7 +5,7 @@ set(LLVM_ENABLE_PROJECTS "clang;lld" CACHE STRING "")
 set(LLVM_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind" CACHE STRING "")
 
 set(LLVM_TARGETS_TO_BUILD Native CACHE STRING "")
-set(BOOTSTRAP_LLVM_BUILD_INSTRUMENTED IR CACHE BOOL "")
+set(BOOTSTRAP_LLVM_BUILD_INSTRUMENTED ON CACHE BOOL "")
 set(CLANG_BOOTSTRAP_TARGETS
   generate-profdata
   stage2