[llvm] [BOLT] Add support for CREL code relocations (PR #196383)

[Amina Chabane via llvm-commits]

Amichaxx wrote:

@aaupov 

> Do we need to ever produce/patch CREL relocations? 
Good point. I've updated to mirror SHT_RELA.

> Can you please test it with e.g. clang built with crel?

I tested with an AArch64 clang built with CREL enabled and linked with `--emit-relocs`. The input has crel, BOLT -relocs enables and the rewritten clang runs.

This patch is motivated by Chromium built with `--emit-relocs` on AArch64. The binary I tested contained relocations in .crel.text rather than .rela.text, so BOLT reported missing code relocations even though they are present in CREL form.

https://github.com/llvm/llvm-project/pull/196383