cmd/dist, cmd/go: pass -arch for C compilation on Darwin

On Apple Silicon Mac, the C compiler has an annoying default
target selection, depending on the ancestor processes'
architecture. In particular, if the shell or IDE is x86, when
running "go build" even with a native ARM64 Go toolchain, the C
compiler defaults to x86, causing build failures. We pass "-arch"
flag explicitly to avoid this situation.

Fixes #43692.
Fixes #43476.
Updates golang/vscode-go#1087.

Change-Id: I80b6a116a114e11e273c6886e377a1cc969fa3f6
Reviewed-on: https://go-review.googlesource.com/c/go/+/283812


Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>