cmd/link: fix checks for supported linker flags with relative paths.
The existing way of checking for supported linker flags causes false negatives
when there are relative paths passed to go tool link. This fixes the issue by
calling the external linker in the current working directory, instead of
in a temporary directory.
Fixes #59952
Change-Id: I173bb8b44902f30dacefde1c202586f87667ab70
Reviewed-on: https://go-review.googlesource.com/c/go/+/491796
Run-TryBot: Cherry Mui <cherryyz@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com>