Make xcb_icccm.h use the same type as icccm.c for win_gravity parameter,
fixes build with PCC which does not use "unsigned int" for enum type

from upstream:

http://cgit.freedesktop.org/xcb/util-old/commit/?id=155c99470961b38ed090ef1b4767c87ec1042386

initial import of xcb-util-0.3.6