win32/detectenv-msvc.mak: Accept Release and Debug as our configs
win32/detectenv-msvc.mak: Accept Release and Debug as our configs

This NMake Makefile can be made usable in MSVC projects, so make lives
for people easier by doing so.

fanc999/gtk-msvc-projects,fanc999/gtk-msvc-projects,fanc999/gtk-msvc-projects,fanc999/gtk-msvc-projects,fanc999/gtk-msvc-projects