[clang] [Clang][CMake] Support perf, LBR, and Instrument CLANG_BOLT options (PR #69133)

[Petr Hosek via cfe-commits]

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@@ -850,23 +850,38 @@ if (CLANG_ENABLE_BOOTSTRAP)
   endforeach()
 endif()
 
-if (CLANG_BOLT_INSTRUMENT AND NOT LLVM_BUILD_INSTRUMENTED)
+set(CLANG_BOLT "INSTRUMENT" CACHE STRING "Apply BOLT optimization to Clang. \
+  May be specified as Instrument or Perf or LBR to use a particular profiling \
+  mechanism.")
+string(TOUPPER "${CLANG_BOLT}" uppercase_CLANG_BOLT)
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petrhosek wrote:

This is a super minor nit, but you can reuse the same variable (it wouldn't actually change the cached value, the non-cached variable is going to shadow the cached one which is fine in this case).

https://github.com/llvm/llvm-project/pull/69133