[release-branch.go1.8] cmd/link: do not pass -s through to host linker on macOS

This keeps the host linker from printing
ld: warning: option -s is obsolete and being ignored

Fixes #19775.

Change-Id: I18dd4e4b3f59cbf35dad770fd65e6baea5a7347f
Reviewed-on: https://go-review.googlesource.com/38851
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-on: https://go-review.googlesource.com/39606
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/link/internal/ld/lib.go

@@ -998,6 +998,10 @@ func (l *Link) hostlink() {
 
 	if !*FlagS && !debug_s {
 		argv = append(argv, "-gdwarf-2")
+	} else if Headtype == obj.Hdarwin {
+		// Recent versions of macOS print
+		//	ld: warning: option -s is obsolete and being ignored
+		// so do not pass any arguments.
 	} else {
 		argv = append(argv, "-s")
 	}