[Xcb] new library for pthread stub functions

[Donnie Berkholz]

Jamey Sharp wrote:
> Another open question is, does a package with 141 lines of source code
> that compiles to a few bytes really need a 300kB gzipped dist tarball?
> It's just possible that autoconf might not be a win here.

I don't think anyone's addressed this part of the mail yet. 300K is 
irrelevant in the bigger picture, especially when you consider that 
developers and source builders (i.e., _not_ most end users) are the only 
people affected.

So although this may not seem like the cleanest end solution, it's 
likely the best overall because of general familiarity with autotools 
and irrelevance of source size to most users.

Thanks,
Donnie