[llvm] [RISCV] Introduce pass to promote double constants to a global array (PR #160536)

[Alex Bradbury via llvm-commits]

asb wrote:

I've set this to merge once pre-commit CI completes, thanks everyone for the reviews. I've additionally added:
* A bailout if we have a fp arg to an intrinsic that is immarg (I don't believe any such intrinsics currently exist, but this is future proof)
* A comment that we would also have problems with inline asm if there was a constraint that required an fp immediate. I don't believe we currently support any such constraints https://llvm.org/docs/LangRef.html#supported-constraint-code-list

https://github.com/llvm/llvm-project/pull/160536