Tell Mesa not to attempt X11 headers

If no X11 related things are being built, tell Mesa's eglplatform.h not to attempt inclusion of associated X11 header.

include/wlr/render/egl.h

@@ -9,6 +9,12 @@
 #ifndef WLR_RENDER_EGL_H
 #define WLR_RENDER_EGL_H
 
+#include <wlr/config.h>
+
+#if !(defined(WLR_HAS_X11_BACKEND) || defined(WLR_HAS_WAYLAND))
+#define MESA_EGL_NO_X11_HEADERS
+#endif
+
 #include <EGL/egl.h>
 #include <EGL/eglext.h>
 #include <pixman.h>

include/wlr/render/interface.h

@@ -9,6 +9,12 @@
 #ifndef WLR_RENDER_INTERFACE_H
 #define WLR_RENDER_INTERFACE_H
 
+#include <wlr/config.h>
+
+#if !(defined(WLR_HAS_X11_BACKEND) || defined(WLR_HAS_WAYLAND))
+#define MESA_EGL_NO_X11_HEADERS
+#endif
+
 #include <EGL/egl.h>
 #include <EGL/eglext.h>
 #include <stdbool.h>