win32/detectenv-msvc.mak: Support Visual Studio 2017
win32/detectenv-msvc.mak: Support Visual Studio 2017

Sync the file from GLib so that we can build the introspection files
using Visual Studio 2017.

GNOME/at-spi2-core,GNOME/at-spi2-core,GNOME/at-spi2-core