[Fontconfig] cross-compiling fontconfig

[Keith Packard]

Around 12 o'clock on Jun 16, Jace Krull wrote:

> but still run into problems during make and make install, when it tries to
> execute the (just built) fc-lang or fc-cache programs.

We'll need to skip this part of the install in a cross compile 
environment; if anyone has suggestions on how to detect that, please speak 
up and we'll try to get it patched.

-keith