When we raise a signal that was delivered to C code, it's possible that
the kernel will not deliver it immediately. This is especially possible
on Darwin where we use send the signal to the entire process rather than
just the current thread. Sleep for a millisecond after sending the
signal to give it a chance to be delivered before we restore the Go
signal handler. In most real cases the program is going to crash at this
point, so sleeping is kind of irrelevant anyhow.

Fixes #14809.

Change-Id: Ib2c0d2c4e240977fb4535dc1dd2bdc50d430eb85
Reviewed-on: https://go-review.googlesource.com/33300
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>