debug: Adds COGL_DEBUG=winsys option
debug: Adds COGL_DEBUG=winsys option

Although we internally had a COGL_DEBUG_WINSYS enum we weren't providing
a way to enable that via the COGL_DEBUG environment variable. This adds
a "winsys" option that can be used to enable printing of winsys debug
notes.

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

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