clutter: Fix broken build for images depending on gobject-introspection-native (e...

clutter: Fix broken build for images depending on gobject-introspection-native (e.g. libwnck_2.30.5 / libgee_0.6.0)

* Error situation:
* 1. configure detects gobject-introspection:
*
configure:12828: checking for gobject-introspection
configure:12859: $PKG_CONFIG --exists --print-errors "gobject-introspection-1.0 >= 0.6.4"
*
* 2. compile fails:
*
  CCLD   libclutter-cogl.la
  GEN    Cogl-1.0.gir
In file included from /home/Superandi/tmp/work/overo-angstrom-linux-gnueabi/clutter-1.2.12-r2.1/clutter-1.2.12/clutter/cogl/cogl/cogl-shader.h:32,
                 from <stdin>:15:
../../../clutter/cogl/cogl/cogl-defines.h:30:23: error: GLES2/gl2.h: No such file or directory
Error while processing the source.
make[7]: *** [Cogl-1.0.gir] Error 1
*
* After fix configure disables gobject-introspection
*
configure:12828: checking for gobject-introspection
configure:12873: result: no (disabled, use --enable-introspection to enable)

Signed-off-by: Andreas Mueller <schnitzeltony@gmx.de>
Signed-off-by: Khem Raj <raj.khem@gmail.com>