runtime: add symbolic constants for freebsd/amd64 syscalls
Brings freebsd/amd64 on par with other OSes/archs.
Updates #53479
Change-Id: I05164c887d776dd4a0ae51eafd4014042b782999
Reviewed-on: https://go-review.googlesource.com/c/go/+/413366 Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Michael Pratt <mpratt@google.com>