[llvm] [clang] [Clang][CMake] Add CSSPGO support to LLVM_BUILD_INSTRUMENTED (PR #79942)

[Aiden Grossman via cfe-commits]

boomanaiden154 wrote:

Do you have benchmarks on how well this performs relative to standard IRPGO (or on top of it)?

https://github.com/llvm/llvm-project/pull/79942