Disable broken signal handler which locks the malloc mutex recursively.

What's happening here is that gnome-shell wants to print a gjs stack
trace when certain signals are caught, and sets up a signal handler
which uses stdio and malloc. This isn't safe.

For now, just disable this signal handler, which will always crash
on OpenBSD rather than producing stack trace information, to prevent
gnome-shell from littering home directories with useless core dumps.

#0  thrkill () at -:3
#1  0x00000dc8de8ca89e in _libc_abort () at /usr/src/lib/libc/stdlib/abort.c:51
#2  0x00000dc8de93cbba in _rthread_mutex_timedlock (mutexp=Variable "mutexp" is 
not available.
)
    at /usr/src/lib/libc/thread/rthread_mutex.c:117
#3  0x00000dc8de8adf12 in malloc (size=128)
    at /usr/src/lib/libc/stdlib/malloc.c:1253
#4  0x00000dc8de947746 in _libc_vasprintf (str=0xdc9b1be0b08, 
    fmt=0xdc935649217 "== Stack trace for context %p ==\n", ap=0xdc9b1be0ce0)
    at /usr/src/lib/libc/stdio/vasprintf.c:39
#5  0x00000dc975b5cbbd in g_vasprintf (string=0xdc9b1be0b08, 
    format=0xdc935649217 "== Stack trace for context %p ==\n", 
    args=0xdc9b1be0ce0) at ../glib-2.58.3/glib/gprintf.c:330
#6  0x00000dc975b13661 in g_strdup_vprintf (
    format=0xdc935649217 "== Stack trace for context %p ==\n", 
    args=0xdc9b1be0ce0) at ../glib-2.58.3/glib/gstrfuncs.c:514
#7  0x00000dc975aef17f in g_printerr (
    format=0xdc935649217 "== Stack trace for context %p ==\n")
    at ../glib-2.58.3/glib/gmessages.c:3247
#8  0x00000dc935781742 in gjs_context_print_stack_stderr ()
   from /usr/local/lib/libgjs.so.5.0
#9  0x00000dc9357817c5 in gjs_dumpstack () from /usr/local/lib/libgjs.so.5.0
#10 0x00000dc6bd8b62f0 in dump_gjs_stack_on_signal_handler (signo=6)

Index: src/main.c
--- src/main.c.orig
+++ src/main.c
@@ -356,6 +356,7 @@ dump_gjs_stack_on_signal_handler (int signo)
 static void
 dump_gjs_stack_on_signal (int signo)
 {
+#if 0 /* this handler is disabled because it triggers malloc mutex recursion */
   struct sigaction sa = {
     .sa_flags   = SA_RESETHAND | SA_NODEFER,
     .sa_handler = dump_gjs_stack_on_signal_handler,
@@ -365,6 +366,7 @@ dump_gjs_stack_on_signal (int signo)
 
   sigaction (signo, &sa, NULL);
   _tracked_signals[signo] = TRUE;
+#endif
 }
 
 static gboolean