[PATCH][demos] configure: Make sure WAYLAND_SCANNER_RULES is defined

[Cyril Brulebois]

If wayland-scanner.m4 is missing, the WAYLAND_SCANNER_RULES macro is
undefined, and this token ends up in the generated configure script.
This makes autogen.sh (or autoreconf) succeed, but configure fail.

Catch that at configure time, making sure the macro was expanded:
| configure.ac:111: error: possibly undefined macro: WAYLAND_SCANNER_RULES
|       If this token and others are legitimate, please use m4_pattern_allow.
|       See the Autoconf documentation.
---
 configure.ac |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/configure.ac b/configure.ac
index 6edf41d..cd97a5a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -109,6 +109,7 @@ fi
 AC_SUBST(GCC_CFLAGS)
 
 WAYLAND_SCANNER_RULES(['$(top_srcdir)/protocol'])
+m4_pattern_forbid([^WAYLAND_SCANNER_RULES$])
 
 AC_CONFIG_FILES([Makefile
 		 compositor/Makefile
-- 
1.7.5.4