cmd/link: fix StackCheckOutput on AIX
This test forces GOARCH to amd64, but currently uses the default GOOS.
This works on every OS that supports amd64, which is every OS we
support except AIX. Hence, on AIX this fails with an unsupported
GOOS/GOARCH combination.
Fix this by forcing GOOS to linux.
Fixes #52451.
Change-Id: I9321dd6386c7ef0fe2b47d77ed900aafc53f2a46
Reviewed-on: https://go-review.googlesource.com/c/go/+/401334
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Austin Clements <austin@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>