glapi: add KHR_no_error support to dispatch table generation

glapi: add KHR_no_error support to dispatch table generation

This will allows us to create no error versions of functions
noted by a _no_error suffix. We also need to set a no_error
attribute equal to "true" in the xml.

V3: stop the no_error attribute being overwritten when functions
    alias another.
V2: tidy up suggested by Nicolai.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>