cmd/objdump: disable external linking test on openbsd/arm

Disable disassembly with external linking test on openbsd/arm, since this
platform does not currently support cgo/external linking.

Change-Id: I6eab6fcaac21407ce05075a4a1407fbfe0e6142b
Reviewed-on: https://go-review.googlesource.com/9481Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/objdump/objdump_test.go

@@ -126,5 +126,9 @@ func TestDisasmExtld(t *testing.T) {
 	case "arm64":
 		t.Skipf("skipping on %s, issue 10106", runtime.GOARCH)
 	}
+	// TODO(jsing): Renable once openbsd/arm has external linking support.
+	if runtime.GOOS == "openbsd" && runtime.GOARCH == "arm" {
+		t.Skip("skipping on openbsd/arm, no support for external linking, issue 10619")
+	}
 	testDisasm(t, "-ldflags=-linkmode=external")
 }