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From 62f053c19b917a369c4aad5b71ab150911b589aa:

xcb-xinput code was produced by build of libxcb 1.13 with xcb-proto 1.13.

The following parts were removed from it:
 - Pointer Barriers API (requires xcb-xfixes 1.9 with xcb-proto 1.9)
 - SendExtensionEvent API (requires definition of xcb_raw_generic_event_t
   from libxcb 1.13)

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As of time of writing the minimal required libxcb version is 1.11, hence
we could restore the Pointer Barriers API, but we don't use it, so it is
not worth the hustle. When we will bump the minimal required version of libxcb
to 1.13, then we can drop the bundled xcb-xinput altogether.

The xcb-xinput files where modified to use system includes, see:

src/3rdparty/xcb/include/xcb/fixup-xinput-h.patch
src/3rdparty/xcb/libxcb/fixup-xinput-c.patch

