runtime: disable TestSetPanicOnFault for dragonfly/386

This test currently deadlocks on dragonfly/386.

Update #7421

LGTM=minux.ma
R=golang-codereviews, minux.ma
CC=golang-codereviews
https://golang.org/cl/69380043

src/pkg/runtime/runtime_test.go

@@ -135,6 +135,12 @@ func TestStopCPUProfilingWithProfilerOff(t *testing.T) {
 }
 
 func TestSetPanicOnFault(t *testing.T) {
+	// This currently results in a fault in the signal trampoline on
+	// dragonfly/386 - see issue 7421.
+	if GOOS == "dragonfly" && GOARCH == "386" {
+		t.Skip("skipping test on dragonfly/386")
+	}
+
 	old := debug.SetPanicOnFault(true)
 	defer debug.SetPanicOnFault(old)