win32/detectenv-msvc.mak: Make it usable from Visual Studio projects
win32/detectenv-msvc.mak: Make it usable from Visual Studio projects

As in the version in of this NMake Makefile module in G-I, support
CFG == Release|Debug, which is what is used in the Visual Studio
projects, so that:

-This file will be in sync with the one in G-I
-Other projects that make use of this can integrate this NMake Makefile
 module in their Visual Studio project files.

johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,endlessm/glib,endlessm/glib