[llvm] Spill/restore FP/BP around instructions in which they are clobbered (PR #81048)

[via llvm-commits]

weiguozhi wrote:

> Since this is currently only handling x86, should we keep it in the x86 target for now, and try to generalize later (maybe with some input from an aarch64 owner)?

I will move it to x86 backend for this initial version. Then many of the callbacks can be removed.

https://github.com/llvm/llvm-project/pull/81048