[clang] [llvm] [Clang][CodeGen] Add -gbtf: target-independent BTF emission for ELF targets (PR #183929)

[Fangrui Song via cfe-commits]

MaskRay wrote:

Note: I don't review BPF/BTF patches. I only make drive-by comments to ensure it is consistent with the components I mainly focus on.

https://github.com/llvm/llvm-project/pull/183929