GH-126910: reserve FP on AArch64 when generating JIT stencils

[diegorusso]

This is a follow up of #143548

This is needed for #146071

• Issue: Supporting stack unwinding in the JIT compiler #126910

[brandtbucher]

Cool! Two questions:

• Has anyone actually tested that this works (and is necessary) for unwinding on macOS or Windows? If not, I'd be inclined to drop those from this PR.
• why -fno-unwind-table everywhere now?

[diegorusso]

• why -fno-unwind-table everywhere now?

Fair point. Without it, stencils generation fails on Darwin because they introduce new relocation like ARM64_RELOC_SUBTRACTOR

On Darwin, -fno-asynchronous-unwind-tables is not enough by itself: clang can still emit .cfi_* in the assembly and produce __compact_unwind / __eh_frame in the object.

I thought to put it everywhere because the JIT stencils do not use object-file unwind metadata at all.

If you prefer I can put it on Darwin AArch64 only.

[diegorusso]

Cool! Two questions:

• Has anyone actually tested that this works (and is necessary) for unwinding on macOS or Windows? If not, I'd be inclined to drop those from this PR.
• why -fno-unwind-table everywhere now?

I've update the PR to do it just on Linux AArch64. macOS requires more investigation as the code generation is slightly different.
I've removed the -fno-unwind-table as well.