Add guards to project files to prevent unnecessarily processing on Windows.

On Windows with default debug_and_release configuration project
files parsed tree times while generating Makefile, Makefile.Debug
and Makefile.Release. Some operation needs only one time processing.

Change-Id: I02d04076cbb70c705916703526444585e83a24ff
Reviewed-by: Andras Becsi <andras.becsi@digia.com>