libgnt/libgnt

Allow introspection on Windows.

2020-11-16, Elliott Sales de Andrade
741097e10968
Allow introspection on Windows.

msys2 supports it, so no need to block it, especially as our other project do
not.

Reviewed at https://reviews.imfreedom.org/r/222/
option('doc', type : 'boolean', value : true, yield : true,
description : 'build documentation with gtk-doc')
option('introspection', type : 'boolean', value : true, yield : true,
description : 'build introspection data')