G_STATIC_ASSERT uses a typedef _GStaticAssertCompileTimeAssertion_1 which is later unused, and fails to build with -Werror on gcc 4.8:

/usr/include/glib-2.0/glib/gmacros.h:162:53: warning: typedef ‘_GStaticAssertCompileTimeAssertion_0’ locally defined but not used [-Wunused-local-typedefs]
 #define G_STATIC_ASSERT(expr) typedef char G_PASTE (_GStaticAssertCompileTimeAssertion_, __COUNTER__)[(expr) ? 1 : -1]
                                                     ^
/usr/include/glib-2.0/glib/gmacros.h:159:47: note: in definition of macro ‘G_PASTE_ARGS’
 #define G_PASTE_ARGS(identifier1,identifier2) identifier1 ## identifier2
                                               ^
/usr/include/glib-2.0/glib/gmacros.h:162:44: note: in expansion of macro ‘G_PASTE’
 #define G_STATIC_ASSERT(expr) typedef char G_PASTE (_GStaticAssertCompileTimeAssertion_, __COUNTER__)[(expr) ? 1 : -1]
                                            ^
/usr/include/glib-2.0/glib/gthread.h:234:5: note: in expansion of macro ‘G_STATIC_ASSERT’
     G_STATIC_ASSERT (sizeof *(location) == sizeof (gpointer));       \
     ^
/usr/include/glib-2.0/gobject/gtype.h:1463:7: note: in expansion of macro ‘g_once_init_enter’
   if (g_once_init_enter (&g_define_type_id__volatile))  \
       ^
/usr/include/glib-2.0/gobject/gtype.h:1294:56: note: in expansion of macro ‘_G_DEFINE_TYPE_EXTENDED_BEGIN’
 #define G_DEFINE_TYPE_WITH_CODE(TN, t_n, T_P, _C_)     _G_DEFINE_TYPE_EXTENDED_BEGIN (TN, t_n, T_P, 0) {_C_;} _G_DEFINE_TYPE_EXTENDED_END()
                                                        ^
/home/mcr2010/src/bzr/compiz/gtk/window-decorator/gwd-settings-notified.c:51:1: note: in expansion of macro ‘G_DEFINE_TYPE_WITH_CODE’
 G_DEFINE_TYPE_WITH_CODE (GWDSettingsNotifiedImpl, gwd_settings_notified_impl, G_TYPE_OBJECT,
 ^
/usr/include/glib-2.0/glib/gmacros.h:162:53: warning: typedef ‘_GStaticAssertCompileTimeAssertion_1’ locally defined but not used [-Wunused-local-typedefs]
 #define G_STATIC_ASSERT(expr) typedef char G_PASTE (_GStaticAssertCompileTimeAssertion_, __COUNTER__)[(expr) ? 1 : -1]
                                                     ^
/usr/include/glib-2.0/glib/gmacros.h:159:47: note: in definition of macro ‘G_PASTE_ARGS’
 #define G_PASTE_ARGS(identifier1,identifier2) identifier1 ## identifier2
                                               ^
/usr/include/glib-2.0/glib/gmacros.h:162:44: note: in expansion of macro ‘G_PASTE’
 #define G_STATIC_ASSERT(expr) typedef char G_PASTE (_GStaticAssertCompileTimeAssertion_, __COUNTER__)[(expr) ? 1 : -1]
                                            ^
/usr/include/glib-2.0/glib/gatomic.h:136:5: note: in expansion of macro ‘G_STATIC_ASSERT’
     G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer));                 \
     ^
/usr/include/glib-2.0/glib/gthread.h:236:7: note: in expansion of macro ‘g_atomic_pointer_get’
     (!g_atomic_pointer_get (location) &&                             \
       ^
/usr/include/glib-2.0/gobject/gtype.h:1463:7: note: in expansion of macro ‘g_once_init_enter’
   if (g_once_init_enter (&g_define_type_id__volatile))  \
       ^
/usr/include/glib-2.0/gobject/gtype.h:1294:56: note: in expansion of macro ‘_G_DEFINE_TYPE_EXTENDED_BEGIN’
 #define G_DEFINE_TYPE_WITH_CODE(TN, t_n, T_P, _C_)     _G_DEFINE_TYPE_EXTENDED_BEGIN (TN, t_n, T_P, 0) {_C_;} _G_DEFINE_TYPE_EXTENDED_END()
                                                        ^
/home/mcr2010/src/bzr/compiz/gtk/window-decorator/gwd-settings-notified.c:51:1: note: in expansion of macro ‘G_DEFINE_TYPE_WITH_CODE’
 G_DEFINE_TYPE_WITH_CODE (GWDSettingsNotifiedImpl, gwd_settings_notified_impl, G_TYPE_OBJECT,
 ^
/usr/include/glib-2.0/glib/gmacros.h:162:53: warning: typedef ‘_GStaticAssertCompileTimeAssertion_2’ locally defined but not used [-Wunused-local-typedefs]
 #define G_STATIC_ASSERT(expr) typedef char G_PASTE (_GStaticAssertCompileTimeAssertion_, __COUNTER__)[(expr) ? 1 : -1]
                                                     ^
/usr/include/glib-2.0/glib/gmacros.h:159:47: note: in definition of macro ‘G_PASTE_ARGS’
 #define G_PASTE_ARGS(identifier1,identifier2) identifier1 ## identifier2
                                               ^
/usr/include/glib-2.0/glib/gmacros.h:162:44: note: in expansion of macro ‘G_PASTE’
 #define G_STATIC_ASSERT(expr) typedef char G_PASTE (_GStaticAssertCompileTimeAssertion_, __COUNTER__)[(expr) ? 1 : -1]
                                            ^
/usr/include/glib-2.0/glib/gthread.h:241:5: note: in expansion of macro ‘G_STATIC_ASSERT’
     G_STATIC_ASSERT (sizeof *(location) == sizeof (gpointer));       \
     ^
/usr/include/glib-2.0/gobject/gtype.h:1477:7: note: in expansion of macro ‘g_once_init_leave’
       g_once_init_leave (&g_define_type_id__volatile, g_define_type_id); \
       ^
/usr/include/glib-2.0/gobject/gtype.h:1294:111: note: in expansion of macro ‘_G_DEFINE_TYPE_EXTENDED_END’
 #define G_DEFINE_TYPE_WITH_CODE(TN, t_n, T_P, _C_)     _G_DEFINE_TYPE_EXTENDED_BEGIN (TN, t_n, T_P, 0) {_C_;} _G_DEFINE_TYPE_EXTENDED_END()
                                                                                                               ^
/home/mcr2010/src/bzr/compiz/gtk/window-decorator/gwd-settings-notified.c:51:1: note: in expansion of macro ‘G_DEFINE_TYPE_WITH_CODE’
 G_DEFINE_TYPE_WITH_CODE (GWDSettingsNotifiedImpl, gwd_settings_notified_impl, G_TYPE_OBJECT,
 ^