Do not save/restore signals around locks.

The unwind code defaults to saving and restoring signals around locks.
Unfortunately, this causes problems with art and dumping the stack
traces of running threads. With this enabled, sometimes the SIGQUIT
signal winds up being unhandled and killing the process instead of
just dumping the thread stack.

Bug: 14229281
Change-Id: I96092f234e84db754ca63032327b0ceb2d2107f0
1 file changed