How to cross-compile a library such as microhttpd.a?

[Bob Furber <burnsmicro@xxxxxxxxx>]

I need to use microhttpd.a and pthread.a to build a cross-compiled 
program to be deployed on an arm-linux-gnueabihf device.

Where can I find instructions on how to do this? Or, is this simply a 
matter of downloading the source code and compiling (on a 64 bit 
UbuntuPC) to a library with my existing gcc-arm-linux-gnueabihf-4.8 
cross-compiler?

While I may be able to find microhttpd.a and pthread.a binaries for an 
arm-linux-gnueabihf device, they will likely have been built with a 
different version of gcc-arm-linux-gnueabihf, which, I fear, could open 
up a can of worms.