internal/gocommand: run 'go list' on the unsafe package when fetching release tags

The specific package we run on doesn't matter, but using unsafe will
be a lot faster than running on whatever package the working directory
is pointing at.

Change-Id: Iae65a262c9bb129f8c8442a72cebf131521357ee
Reviewed-on: https://go-review.googlesource.com/c/tools/+/323390
Trust: Dominik Honnef <dominik@honnef.co>
Run-TryBot: Dominik Honnef <dominik@honnef.co>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
diff --git a/internal/gocommand/version.go b/internal/gocommand/version.go
index 0cebac6..7130436 100644
--- a/internal/gocommand/version.go
+++ b/internal/gocommand/version.go
@@ -14,7 +14,7 @@
 // It returns the X in Go 1.X.
 func GoVersion(ctx context.Context, inv Invocation, r *Runner) (int, error) {
 	inv.Verb = "list"
-	inv.Args = []string{"-e", "-f", `{{context.ReleaseTags}}`}
+	inv.Args = []string{"-e", "-f", `{{context.ReleaseTags}}`, `--`, `unsafe`}
 	inv.Env = append(append([]string{}, inv.Env...), "GO111MODULE=off")
 	// Unset any unneeded flags, and remove them from BuildFlags, if they're
 	// present.