The assumption is that you're using 'g++' as your cpp compiler. If that's not
the case then you need to first amend the 'CC' entry in the Makefile.PL
appropriately.

Inherit.xs and CPP.map were produced by running the Inline::C2XS function:

cpp2xs('Math::Geometry::Planar::GPC::Inherit', 'main');

(It was run against the 'Inherit.cpp' file that is located in the t folder of
this Inline::C2XS source distro.)

For the purposes of providing a complete example of what is needed, I've 
included, in this directory (ie 'demos'), a corresponding pm file, a 
Makefile.PL, a MANIFEST, a README (this file) and a test file (test.pl).

Then cd to the directory containing this file and run:

perl Makefile.PL
make test

You should even be able to then successfully run 'make install' - though,
given that this module doesn't really do anything useful, I don't know why
anyone would want to install it. It's also quite ludicrous to be creating
Inherit.pm in the Math::Geometry::Planar::GPC namespace.

Anyway, this demo works fine for me on Win32 using the MinGW's g++
compiler and MinGW-built perl 5.8.8.

Cheers,
Rob