[clang] Fix objc_sel_{name,types} missing an underscore (PR #88713)

[Jonathan Schleifer via cfe-commits]

Midar wrote:

These symbols are just used to deduplicate strings: That's why they're hidden and in COMDAT. So I don't think it'll break or fix the ABI ;).

https://github.com/llvm/llvm-project/pull/88713