build/gi-introspection-msvc.mak: Fix Include Path

The -I flags for generating GIRepository-2.0.gir should use $(BASEDIR), not
%BASEDIR%, as we are not using a Windows .bat to generate the introspection
files.
cachestore: Use "write new, then rename" pattern, not "write in place"

This should fix race conditions when multiple processes attempt to
access the cache concurrently.

https://bugzilla.gnome.org/show_bug.cgi?id=724886