[llvm] Clarify whether aarch64 supports gc.statepoints

[zero9178]

The documentation (https://llvm.org/docs/Statepoints.html#supported-architectures) currently states that it is only supported for X86_64 , yet by chance I just came across https://reviews.llvm.org/D66012 which seems to have landed some time ago.

The commit message does imply that the transition flag is not supported, but I believe it might be worth documenting either way, if the rest of the functionality works (and seems to be in use by GraalVM)

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

[preames]

I can confirm that Aarch64 supports gc.statepoint. A patch to fix the documentation would be welcomed.