Xnest: tidy up extension blacklisting in miinitext.c

The DDX'es sometimes need to disable certain extensions. Instead of complex
include cascades with ifdef'ed ddx-specific include from dix code, it's
more clean to add some clear and explicit knobs set by the DDX'es individual
meson.build.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1401>

hw/xnest/meson.build

@@ -33,7 +33,7 @@ executable(
         libxserver_xi_stubs,
         libxserver_xkb_stubs,
     ],
-    c_args: '-DHAVE_XNEST_CONFIG_H',
+    c_args: [ '-DHAVE_XNEST_CONFIG_H', '-DDISABLE_EXT_COMPOSITE', '-DDISABLE_EXT_DPMS', '-DISABLE_EXT_MITSHM' ],
     install: true,
 )
 

mi/miinitext.c

@@ -78,12 +78,19 @@ SOFTWARE.
 #include "xf86Extensions.h"
 #endif
 
-#ifdef HAVE_XNEST_CONFIG_H
-#include <xnest-config.h>
+/* some DDXes must explicitly prohibit some extensions */
+#ifdef DISABLE_EXT_COMPOSITE
 #undef COMPOSITE
+#endif
+
+#ifdef DISABLE_EXT_DPMS
 #undef DPMSExtension
 #endif
 
+#ifdef DISABLE_EXT_MITSHM
+#undef MITSHM
+#endif
+
 #include "misc.h"
 #include "extension.h"
 #include "extinit_priv.h"