[CMake][Release] Disable PGO (llvm#88465)

Running the test-release.sh script with PGO enabled causes build errors like: ld.lld: error: Function Import: link error: linking module flags 'ProfileSummary': IDs have conflicting values I believe this a build system bug due to the PGO profile data being generated unconditionally. If you run `ninja check-all` and then `ninja install` like we do in test-release.sh, then the profile data is regenerated during `ninja install` and some of the clang tools which are not test dependencies get build during the ninja install step with different profile data. When these tools link against the LLVM libraries, like libSupport, we end up with these errors.

Author: tstellar

clang/cmake/caches/Release.cmake

@@ -4,7 +4,7 @@
 
 # General Options
 set(LLVM_RELEASE_ENABLE_LTO THIN CACHE STRING "")
-set(LLVM_RELEASE_ENABLE_PGO ON CACHE BOOL "")
+set(LLVM_RELEASE_ENABLE_PGO OFF CACHE BOOL "")
 
 set(CMAKE_BUILD_TYPE RELEASE CACHE STRING "")