Based on riscv-go port.
Updates #27532
Change-Id: If522807a382130be3c8d40f4b4c1131d1de7c9e3
Reviewed-on: https://go-review.googlesource.com/c/go/+/204632
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>