BUG: Handle a version string from a custom-built mingw64.

The custom build compiler "GNU Fortran (rubenvb-4.8.0) 4.8.0" was
incorrectly parsed as version '-4.8.0' and the flag "-mno-cygwin" was
added to the compilation.

See http://cens.ioc.ee/pipermail/f2py-users/2010-October/002092.html.