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

[Amir Ayupov via cfe-commits]

aaupov wrote:

Linking the preprint of the paper accepted to CGO'24 which has a CSSPGO performance comparison with AutoFDO and Instr PGO (Fig. 6): https://htyu.github.io/paper/Revamping_Sampling_based_PGO_with_Context_sensitivity_and_Pseudo_instrumentation_preprint.pdf

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