I noticed this problem when trying to use gdb with mozilla.
I got messages like:

Program received signal ?, Unknown signal.
0x2aeb31bb in __sigsuspend (set=0x7fffebf8)

Continuing at this point seems to hang both gdb and the
app.  In a possibly related matter, I used the command:

handle SIG32 nostop

with gdb 4.17. 4.18 seems to complain that it doesn't know
what SIG32 is.  I think this might be a thread problem
because I am not seeing the [New thread] messages like in
4.17.