Test flags before using "info"

Our debugger signal catcher expects to receive three args, but if
somebody cleared SA_SIGINFO we only get one, and bad things happen
when we try to use the second one.  Test to see if SA_SIGINFO is
still set before we try to use the argument.

(cherry-pick of f84bc8d6f6368f1c846124a8168761ee8cc589c0.)

Bug: 7272866
Change-Id: I69a65c25e833aea70acb78f9ba40ed93308583e6
1 file changed