Post History

The general mechanism you describe has been in use since there were cross-compilers and libraries that were meant to provide the same application interface on different platforms.  Your specific example using XML is newer of course.

Any competent build system has the ability to switch include files and make other modifications based on the target platform.  This is nothing new.

One of the earliest full build systems (and source code control too) that I am aware of was Apollo DSEE, developed in the early 1980s.  In DSEE, you specified the target platform via selecting a "thread".  The various build files could cause different files to be used and command line options changed based on state ultimately derived from the thread.

Before that, people used shell scripts to achieve the same thing, although not as elegantly as full-blown build systems.

This is an ancient concept, probably because it's an obvious solution when faced with the multi-platform build problem.