cmd/objdump: reference tracking bug in TestDisasmCode skip message

Issue #12559 was closed and split into #19158 for mips{,le} and #19156
for mips64{,le}. Instead of referencing the individual GOARCH-specific
issues in the skip test messages of TestDisasmCode use the tracking bug

Change-Id: I6929d25f4ec5aef4f069b7692c4e29106088ce65
Reviewed-on: https://go-review.googlesource.com/c/go/+/209817
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/objdump/objdump_test.go

@@ -176,10 +176,8 @@ func TestDisasm(t *testing.T) {
 
 func TestDisasmCode(t *testing.T) {
 	switch runtime.GOARCH {
-	case "mips", "mipsle", "mips64", "mips64le":
-		t.Skipf("skipping on %s, issue 12559", runtime.GOARCH)
-	case "s390x":
-		t.Skipf("skipping on %s, issue 15255", runtime.GOARCH)
+	case "mips", "mipsle", "mips64", "mips64le", "s390x":
+		t.Skipf("skipping on %s, issue 19160", runtime.GOARCH)
 	}
 	testDisasm(t, true)
 }