[compiler-rt] [AArch64] Implement INIT/ADJUST_TRAMPOLINE (PR #70267)

[Carlos Eduardo Seo via llvm-commits]

ceseo wrote:

> @ceseo Thanks for this patch. Did you see the related patch in Phabricator? https://reviews.llvm.org/D149848

I missed that one. Thanks for pointing that out.

So, I think I agree that it is better to do the same as gcc does. The code will probably be very untidy, since we have to write the actual instructions (like in the x86 implementation), but it should work too.

The only observation I have is that, whatever the approach is, we cannot use `x18` for the nest parameter outside Linux because both macOS and Windows ABIs already assign this register for something else.

If the submitter of that patch wants to do this, I'm OK with that since I'll be away for a month or so.

https://github.com/llvm/llvm-project/pull/70267