Gnome Screensaver refuses to compile if the X Gamma extension is not available (I forgot to install the header files beforehand, that's why I noticed):

make  all-am
make[1]: Entering directory `/home/uws/Projects/Gnome/Development/src/gnome-screensaver/src'
  CC     gs-fade.o
gs-fade.c: In function ‘check_gamma_extension’:
gs-fade.c:443: error: ‘screen_priv’ undeclared (first use in this function)
gs-fade.c:443: error: (Each undeclared identifier is reported only once
gs-fade.c:443: error: for each function it appears in.)
make[1]: *** [gs-fade.o] Error 1
make[1]: Leaving directory `/home/uws/Projects/Gnome/Development/src/gnome-screensaver/src'
make: *** [all] Error 2


This is due to the #ifdef guards not matching correctly:

static void
check_gamma_extension (GSFade *fade, int screen_idx)
{
#ifdef HAVE_XF86VMODE_GAMMA
        struct GSFadeScreenPrivate *screen_priv;
        [...]
#endif
        screen_priv->fade_type = FADE_TYPE_NONE;
}