Re: crash: x_error_quitter

[Richard Stallman]

    The stack frames will usually not get affected.  But the return
    address might be completely wrong, and that will affect gdb's idea of
    what function the stack frame belongs to, and what variables are
    stored in what registers at that point of time.

It probably won't matter, because we aren't going to try to debug the
Xlib functions themselves.  We want to know which Xlib function Emacs
called, and how.

However, we should turn off the NO_RETURN for this.
(It seems to be on x_connection_closed.)

    I think that if we are compiling with -g, we should also enable the
    -fno-crossjumping option.

I always use -O0 -fnoinline, for maximum debuggability.
But that shouldn't matter for this bug.  The backtrace
should give the info we need, presuming (x-synchronize t)
was done.