[cogl] build: Only allow GLX when finding the x11 pc file

[Damien Lespiau <dlespiau src gnome org>]

commit a789107860d7d70138219dc4dc679e564fcf0f92
Author: Damien Lespiau <damien lespiau intel com>
Date:   Thu May 12 11:43:27 2011 +0100

    build: Only allow GLX when finding the x11 pc file
    
    You can refine earlier the ALLOW_GLX variable when enabling OpenGL builds:
    No x11.pc? no GLX!

 configure.ac |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 1c91781..1fda551 100644
--- a/configure.ac
+++ b/configure.ac
@@ -396,7 +396,8 @@ AS_IF([test "x$enable_gl" = "xyes"],
       [
         DRIVER_COUNT=$((DRIVER_COUNT + 1))
         COGL_DRIVER=gl
-        ALLOW_GLX=yes
+
+        PKG_CHECK_EXISTS([x11], [ALLOW_GLX=yes])
 
         cogl_gl_headers="GL/gl.h"