[llvm] [MC] Fuse relaxation and layout into a single forward pass (PR #184544)

[Hans Wennborg via llvm-commits]

zmodem wrote:

While the error is the same, the gemini repro relies on inline asm to trick the backend into underestimating the size of a basic block. `TargetInstrInfo::getInlineAsmLength()` doesn't understand the `.rept` construct, so it underestimates the size, and the cmp+br is incorrectly folded to CBZ.

`getInlineAsmLength()` is never called when compiling prepro.cc however, so inline asm size estimation is not the problem in that case.

https://github.com/llvm/llvm-project/pull/184544