tests/signals: Disable large enumeration value test that is failing on PPC64

Basically due to a combination of va_args semantics around
signed/unsigned ints, this test case fails on ppc64.  At the moment,
we have as yet to find any real-world consumer with such a large
enumeration value.

Unfortunately, the possible fixes for this are extremely invasive;
we would have to define a new enum API.

Given both of these facts, we believe it makes the most sense at the
current time to simply not test this. If we at a later time determine
there is such a real-world consumer, we can look at doing the
necessary fixes.

https://bugzilla.gnome.org/show_bug.cgi?id=686662

gobject/tests/signals.c

@@ -10,7 +10,10 @@ typedef enum {
 
 typedef enum {
   TEST_UNSIGNED_ENUM_FOO = 1,
-  TEST_UNSIGNED_ENUM_BAR = 0x80000000
+  TEST_UNSIGNED_ENUM_BAR = 42
+  /* Don't test 0x80000000 for now- nothing appears to do this in
+   * practice, and it triggers GValue/GEnum bugs on ppc64.
+   */
 } TestUnsignedEnum;
 
 static GType