versioner: compile with `clang -include foo.h -`.

At least one warning only triggers in files that are included, instead
of being passed directly. Switch to compiling with -include, and fix
the resulting warnings.

Bug: https://github.com/android-ndk/ndk/issues/474
Test: mma -j && versioner
Test: python tools/versioner/run_tests.py
Change-Id: I784698c18540c9cc30f372f279a1cec1d75721ea