[Pixman] Build system patches for threading.

[M Joonas Pihlaja]

On Sun, 11 Jul 2010, Luca Barbato wrote:

> I wonder if acx_pthread.m4 couldn't been used instead of replicating the
> effort.

We've tried that on the cairo side and while it's been giving us some 
success over defaulting to "-pthread" everywhere, it's also causing 
some grief.  So far the strategy of using "-D_REENTRANT -lpthread" or 
"-pthread", in that order, has got us covered on the systems we're 
compiling on.

Cheers,

Joonas