[lld] [lld][ELF] Extend profile guided function ordering to ELF binaries (PR #117514)

[Peter Smith via llvm-commits]

smithp35 wrote:

Just a quick drive by comment on the ELF side, I've not had a chance to go through the code in detail. I think the .subsections_via_symbols is MachO specific. Not quite sure what it does in ELF. I think the equivalent in clang at least is -ffunction-sections and for data -fdata-sections. For assembler the user has to be careful to make a section per function.

If I'm right it could be worth updating comments and the assembler test.

https://github.com/llvm/llvm-project/pull/117514