Don't use XFreeXDGA to determine DGA support

If our server supports DGA and we want to build the dummy driver without it,
XFreeXDGA will be defined by the server and will be picked up rather than
our configuration option.  This change forces us to honor our configuration
hoice.

Signed-off-by: Jeremy Huddleston <jeremyhu@apple.com>

configure.ac

@@ -61,7 +61,7 @@ XORG_DRIVER_CHECK_EXT(XV, videoproto)
 
 if test "x$DGA" = xyes; then
 	XORG_DRIVER_CHECK_EXT(XFreeXDGA, xf86dgaproto)
-	AC_DEFINE(XFreeXDGA, 1, [Support DGA extension])
+	AC_DEFINE(USE_DGA, 1, [Support DGA extension])
 fi
 AC_SUBST([DGA])
 AM_CONDITIONAL([DGA], [test "x$DGA" = xyes])

src/dummy_driver.c

@@ -45,7 +45,7 @@
 #include <X11/Xproto.h>
 #include "scrnintstr.h"
 #include "servermd.h"
-#ifdef XFreeXDGA
+#ifdef USE_DGA
 #define _XF86DGA_SERVER_
 #include <X11/extensions/xf86dgaproto.h>
 #endif
@@ -592,7 +592,7 @@ DUMMYScreenInit(int scrnIndex, ScreenPtr pScreen, int argc, char **argv)
 
     xf86SetBlackWhitePixels(pScreen);
 
-#ifdef XFreeXDGA
+#ifdef USE_DGA
     DUMMYDGAInit(pScreen);
 #endif