runtime: install SIGURG handler on C created threads

Precise stack scan uses SIGURG to trigger a stack scan. We need
to have Go signal handler installed for SIGURG.

Change-Id: I08af281304aee13a7f37ed0654a985a31a5fe024
Reviewed-on: https://go-review.googlesource.com/c/159097
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed