runtime: sleep longer in dieFromSignal on Darwin

Fixes #20315

Change-Id: I5d5c82f10902b59168fc0cca0af50286843df55d
Reviewed-on: https://go-review.googlesource.com/82375
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/signal_unix.go

@@ -432,6 +432,14 @@ func dieFromSignal(sig uint32) {
 	osyield()
 	osyield()
 
+	// On Darwin we may still fail to die, because raise sends the
+	// signal to the whole process rather than just the current thread,
+	// and osyield just sleeps briefly rather than letting all other
+	// threads run. See issue 20315. Sleep longer.
+	if GOOS == "darwin" {
+		usleep(100)
+	}
+
 	// If we are still somehow running, just exit with the wrong status.
 	exit(2)
 }