For some cross-platform examples, we need to tweak things based on the target platform. For this reason, target identification needs to happen early, before inclusion of the top-level Makefile.include. Up to now, we have simply replicated the target-identification code to example Makefiles, leading to code-replication and on occasion bugs (incorrect platform identification).
This commits moves the correct working code to a separate file, so that example Makefiles can include this "as a library". The top-level Makefile merely includes this file now.
