runtime: add async preemption support on riscv64
This CL adds support of call injection and async preemption on
riscv64. We also clobbered REG_TMP for the injected call. Unsafe
points related to REG_TMP access have been marked in previous commits.
Fixes #36711.
Change-Id: I1a1df5b7fc23eaafc34a6a6448fcc3c91054496e
GitHub-Last-Rev:
f6110d470713be70d960fd3e984fea89bb371719
GitHub-Pull-Request: golang/go#38146
Reviewed-on: https://go-review.googlesource.com/c/go/+/226206
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Joel Sing <joel@sing.id.au>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>