Configuration system refactor

More flexible than the prior version and in particular allows cross-compilation.

The native build was tested on win64 with Windows SDK 7.1 and Strawberry Perl 5.16x and the cross build from Cygwin32 to MinGW64.

The environment and compiler settings (beginning of `Configure.pl`) need some tweaking - in particular, the linux flags probably miss a `-luuid`.

Feedback from all available platforms (in particular linux, darwin, bsd) would be appreciated.

As a side note, this also makes APR compilation on MinGW64 mostly work - they do some creative stuff with winapi header inclusion order, which makes it necessary to twiddle with `<wtypes.h>` after the build aborts.

This request is reviewed best by looking at [`build/Makefile.in`](https://github.com/gerdr/MoarVM/blob/gerdr/configure/build/Makefile.in) and [`Configure.pl`](https://github.com/gerdr/MoarVM/blob/gerdr/configure/Configure.pl).