These registers are not available for programs to use. Prior to this
change, the compiler would crash attempting to use ZR as a general
purpose register. Other programs would compile but on execution would
overwrite the G register and cause havoc.
Fixes linux/arm64 build.
Fixes#10304Fixes#10320
Change-Id: I5cf51d3b77cfe3db7dd6377324950cafb02f8d8b
Reviewed-on: https://go-review.googlesource.com/8456
Reviewed-by: Minux Ma <minux@golang.org>
