various tests: do not provoke SIGTRAP with -m no-undefined

Some of the GLib tests deliberately provoke warnings (or even fatal
errors) in a forked child. Normally, this is fine, but under valgrind
it's somewhat undesirable. We do want to follow fork(), so we can check
for leaks in child processes that exit gracefully; but we don't want to
be told about "leaks" in processes that are crashing, because there'd
be no point in cleaning those up anyway.

https://bugzilla.gnome.org/show_bug.cgi?id=666116

gobject/tests/ifaceproperties.c

@@ -615,6 +615,9 @@ base2_object_init (Base2Object *object)
 static void
 test_not_overridden (void)
 {
+  if (!g_test_undefined ())
+    return;
+
   g_test_bug ("637738");
 
   if (g_test_trap_fork (0, G_TEST_TRAP_SILENCE_STDOUT|G_TEST_TRAP_SILENCE_STDERR))