cmd/link: disable DWARF when not generating symtab

Fixes #15166

Change-Id: I30284e3c0fb2c80b26a2572e2fb249b8018e85f9
Reviewed-on: https://go-review.googlesource.com/21587
Run-TryBot: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -1915,6 +1915,9 @@ func dwarfgeneratedebugsyms() {
 	if Debug['w'] != 0 { // disable dwarf
 		return
 	}
+	if Debug['s'] != 0 && HEADTYPE != obj.Hdarwin {
+		return
+	}
 	if HEADTYPE == obj.Hplan9 {
 		return
 	}