runtime: mark memequal and memclrNoHeapPointers nosplit

They are wrappers of libc functions that use no stack. Mark them
nosplit so the linker won't patch it to call __morestack_non_split.

Change-Id: Ib649f9162d0d69cd20f6a283a763a634ad112967
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/183629
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2 files changed