glapi: work-around MSVC 65K string length limitation for enums.c

glapi: work-around MSVC 65K string length limitation for enums.c

String literals cannot exceed 65535 characters for MSVC.  Instead of
emiting a string, emit an array of characters.

v2: fix indentation and add comment in the gl_enums.py file about this
ugliness.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>