[llvm] [BOLT][AArch64] Add call relaxation pass (PR #173952)

[Adam Bzowski via llvm-commits]

adam-bzowski-arm wrote:

While working on #218232, I tested the experimental relaxation introduced here against several layout-sensitive cases. I found configurations where a direct call remains out of range, producing either an MC fixup error or a JITLink `Branch26PCRel` error. I collected the reproducers and analysis here: #218885.

https://github.com/llvm/llvm-project/pull/173952