updates for libxcb / xcb-proto 1.17.0.

build fixes and updates for libxcb / xcb-proto 1.12.

update for libxcb 1.11.

update the libxcb generated files from libxcb 1.9

build support for libxcb 1.6. not yet used.

XXX: i couldn't get the python/xml generator to run outside of
XXX: the libxcb build tree, so i just copied these from there,
XXX: but ideally files/Make

build support for libxcb 1.6. not yet used.

XXX: i couldn't get the python/xml generator to run outside of
XXX: the libxcb build tree, so i just copied these from there,
XXX: but ideally files/Makefile could know how to do this.

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