configure: Expose COGL_HAS_GLX_SUPPORT publicly
configure: Expose COGL_HAS_GLX_SUPPORT publicly

Instead of only exposing COGL_HAS_GLX_SUPPORT internally in config.h we
now expose it though the public cogl-defines.h header.

Signed-off-by: Neil Roberts <822ec91a7ef82248fd36162ca8ac3283eba70848@linux.intel.com>

spatulasnout/cogl,djdeath/cogl,gcampax/cogl,collects/cogl,gcampax/cogl,djdeath/cogl,Distrotech/cogl,djdeath/cogl,Distrotech/cogl,Distrotech/cogl,spatulasnout/cogl,djdeath/cogl-android,gcampax/cogl,djdeath/cogl-android,djdeath/cogl-android,Distrotech/cogl,collects/cogl,gcampax/cogl