The freebsd/riscv64 port was added in go1.20, make cmd/api aware of it and
backfill API files.
For #58582
Change-Id: I242b161cdb6221c8f60a1868c6435be26fca0078
Reviewed-on: https://go-review.googlesource.com/c/go/+/469135
Run-TryBot: Dmitri Goutnik <dgoutnik@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Bryan Mills <bcmills@google.com>