scannerlexer.l: Update to Support MSVC Preprocessor

This updates giscanner/scannerlexer.l by ignoring the Visual C++-specific
directives, so that the scanner will not bail out while trying to produce
the introspection dumper program source code, and silence many of the
warnings that are produced in the process.

As the Visual C++ processor produces slightly different line markers, we
need to handle this here as well, otherwise the sources/headers would not
be processed to acquire the _get_type and _get_gtype symbols to put in the
introspection dumper sources, producing bad results.

https://bugzilla.gnome.org/show_bug.cgi?id=728313