Fix version parse error from a personal build of GCC

I tried using GCC from this source http://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win64/Personal%20Builds/rubenvb/

which has a version string:
```
GNU Fortran (rubenvb-4.8.0) 4.8.0
```

This was incorrectly determined a version ``-4.8.0``, and added ``-mno-cygwin`` to the compile flags, which are no longer accepted.

See related: http://cens.ioc.ee/pipermail/f2py-users/2010-October/002092.html