FindX11: Add even more xcb components

Since we're already shipping some of the xcb modules in FindX11, I figured that we might as well ship all of them. This includes many useful modules that weren't already included (xcb_xcomposite, xcb_errors, xcb_ewmh) as well as some completely useless ones (xcb_glx, xcb_xvmc). Some of them could have been omitted, but I figured that being comprehensive and letting clients decide what to include is preferred over being judicious.

N.B. I'd like to add some more cases to FindX11's main.c but I couldn't figure out how to get the test to build and run properly. It doesn't build with the general test suite, and when building it inside its own directory it compiled with no errors when I put invalid code inside of some of the #ifdef blocks that should have been defined. Perhaps the HAVE_* variables aren't getting passed down correctly?