Rename testsrules_msvc.mak to detectenv_msvc.mak and remove some package-
specific stuff from it, to reflect on the nature that this NMake Makefile
is shared.
The current approach of building the introspection files for GTK works, but
is often cumbersome as one needs to set many environmental variables before
launching a solution file, which runs a Windows batch script to generate
the .gir/.typelib files. It was also possible to hand-run the batch script
from the Visual Studio command prompt, but even more environmental
variables need to be set.
This changes the approach to build the introspection files using an NMake
Makefile (but elimating from the Visual Studio Project Files the part to
build the introspection files) to:
-Make it clearer to the person building the introspection files what
environmental variables are needed, specifically for PKG_CONFIG_PATH and
MINGWDIR and CFG (formerly CONF). Setting stuff like VSVER, PLAT and BASEDIR
is no longer required, which was a bit clunky.
-Allows some more easier flexibility on the build of the intropsection files.
