modules/gnome.py: Fix generating .gir with latest Windows SDK

[fanc999-1]

...when a Visual Studio-style compiler is being used.

The dumper program will fail to link with an obscure undefined symbol 'guard_check_icall$fo$' without an appropriate CRT cflag (i.e. /MD or /MDd for instance) specified, when the latest Windows SDK (10.0.26100.0 or later) is being used on Visual Studio 2019 at least.

This applies the appropriate CRT cflag according to the build options during introspection scanning so that this issue will be avoided.