This adds a configurable path for pkg-config, in case it is not in the
PATH, which will replace the entry in introspection-msvc.mak eventually.
Also add a set of preprocessor flags for GDK that we can use later for
introspection.
Fix the previous commit as the default PREFIX is missing a layer of
parentdir.
...instead of in the gtk-3 project. This will also make the project
files a bit cleaner. Note that this commit only moves all the source
code generating steps in the gtk-3 into the NMake Makefile, and so
generate those sources in the gtk3-prebuild project.
With the exception of the enumeration sources (gdkenumtypes.h and
gdkenumtypes.c), the generared sources in gdk/ (gdkversionmacros.h,
gdkresources.[c|h], gdkmarshalers.[c|h] are now generated in the
gtk3-prebuild projects with the NMake Makefiles.
Make build/win32/config-msvc.mak filled with the version info from
autotools, too.
