configure: Use WAYLAND_SCANNER_RULES only if available

This has the drawback that when creating configure for
distribution, wayland needs to be available for the packager.

Also the the macros has the wayland prefix hardcoded, so
we cant copy it in mesa right now.

configure.ac

@@ -1710,7 +1710,8 @@ yes)
 				  [AC_MSG_ERROR([cannot find libwayland-client])])
                 GALLIUM_WINSYS_DIRS="$GALLIUM_WINSYS_DIRS sw/wayland"
 
-                WAYLAND_SCANNER_RULES(['$(top_srcdir)/src/egl/wayland/wayland-drm/protocol'])
+                m4_ifdef([WAYLAND_SCANNER_RULES],
+                         [WAYLAND_SCANNER_RULES(['$(top_srcdir)/src/egl/wayland/wayland-drm/protocol'])])
 	fi
         if test "$plat" = "drm" && test "x$enable_gbm" = "xno"; then
                 AC_MSG_ERROR([EGL platform drm needs gbm])