[PGO] Allow overriding -vp-counters-per-site

[tambre]

Summary

In some build configurations more than 1.5 might be required.
Paramaterize so it can be changed by the user.

llvm/cmake/modules/HandleLLVMOptions.cmake

append("-fexperimental-new-pass-manager"
     CMAKE_EXE_LINKER_FLAGS
     CMAKE_SHARED_LINKER_FLAGS)
 endif()
 
 option(LLVM_ENABLE_IR_PGO "Build LLVM and tools with IR PGO instrumentation (deprecated)" Off)
 mark_as_advanced(LLVM_ENABLE_IR_PGO)
 
 set(LLVM_BUILD_INSTRUMENTED OFF CACHE STRING "Build LLVM and tools with PGO instrumentation. May be specified as IR or Frontend")
-mark_as_advanced(LLVM_BUILD_INSTRUMENTED)
+set(LLVM_VP_COUNTERS_PER_SITE "1.5" CACHE STRING "Value profile counters to use per site for IR PGO with Clang")
+mark_as_advanced(LLVM_BUILD_INSTRUMENTED LLVM_VP_COUNTERS_PER_SITE)
 string(TOUPPER "${LLVM_BUILD_INSTRUMENTED}" uppercase_LLVM_BUILD_INSTRUMENTED)
 
 if (LLVM_BUILD_INSTRUMENTED)
   if (LLVM_ENABLE_IR_PGO OR uppercase_LLVM_BUILD_INSTRUMENTED STREQUAL "IR")
     append("-fprofile-generate=\"${LLVM_PROFILE_DATA_DIR}\""
       CMAKE_CXX_FLAGS
       CMAKE_C_FLAGS)
     if(NOT LINKER_IS_LLD_LINK)
         append("-fprofile-generate=\"${LLVM_PROFILE_DATA_DIR}\""
           CMAKE_EXE_LINKER_FLAGS
           CMAKE_SHARED_LINKER_FLAGS)
     endif()
     # Set this to avoid running out of the value profile node section
     # under clang in dynamic linking mode.
     if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND
         CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 11 AND
         LLVM_LINK_LLVM_DYLIB)
-      append("-Xclang -mllvm -Xclang -vp-counters-per-site=1.5"
+      append("-Xclang -mllvm -Xclang -vp-counters-per-site=${LLVM_VP_COUNTERS_PER_SITE}"
         CMAKE_CXX_FLAGS
         CMAKE_C_FLAGS)
     endif()
   elseif(uppercase_LLVM_BUILD_INSTRUMENTED STREQUAL "CSIR")
     append("-fcs-profile-generate=\"${LLVM_CSPROFILE_DATA_DIR}\""
       CMAKE_CXX_FLAGS
       CMAKE_C_FLAGS)
     if(NOT LINKER_IS_LLD_LINK)