XCB: allow building without xcb-utils
XCB: allow building without xcb-utils

Of xcb-utils, we only use xcb-keysms at the moment. xcb-keysyms is only
needed for the globalhotkeys and xcb_window plugins. If there is another
window provider plugin, we can do without them so long as the user does
not set --no-embedded-video.

Note: xcb-utils is still needed for the LibVLC embedded video as it
depends on xcb_window. We could  #ifdef the key press support in
xcb_window if this is an issue (I didn't bother).

jomanmuk/vlc-2.1,krichter722/vlc,vlc-mirror/vlc,vlc-mirror/vlc-2.1,vlc-mirror/vlc-2.1,vlc-mirror/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.2,krichter722/vlc,krichter722/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,jomanmuk/vlc-2.2,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,krichter722/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc,jomanmuk/vlc-2.1,jomanmuk/vlc-2.1,xkfz007/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,shyamalschandra/vlc,xkfz007/vlc,shyamalschandra/vlc,krichter722/vlc,krichter722/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,vlc-mirror/vlc-2.1,krichter722/vlc,shyamalschandra/vlc,vlc-mirror/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,vlc-mirror/vlc,xkfz007/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,jomanmuk/vlc-2.2,xkfz007/vlc