[llvm] [RISCV][WIP] Branch to Absolute Address (PR #133555)

[Alex Bradbury via llvm-commits]

asb wrote:

> [Craig reminded me of this recently](https://github.com/llvm/llvm-project/pull/131996#discussion_r2004045898) and Ana mentioned that there had been previous discussions about this, but did not recall the resolution.

My recollection is there were no objections to making the change, but nobody was hugely motivated to do so. Looks like you've solved the latter problem!

IIRC there's inconsistency both within LLVM for branch to absolute address, and even across LLVM and binutils for the same targets. But matching binutils and updating tests to use `. +` for the old behaviour makes sense to me.

My expectation is that making the change shouldn't be disruptive externally because the main users who rely on the current behaviour would be us with the MC tests, and potentially other external test suites (e.g. using the assembler to help with instruction decoder tests). For the latter, for binutils compatibility they would have had to be using `. +` anyway. If anyone thinks the impact may be broader, please do speak up!

https://github.com/llvm/llvm-project/pull/133555