gnutls 3.0.4 and mingw-w64 build issues

[Hoyt, David]

> [...] headers being included that don't exist with mingw-w64. e.g.:

gnulib does provide the following:

sys/select.h: http://www.gnu.org/s/hello/manual/gnulib/sys_002fselect_002eh.html
arpa/inet.h: http://www.gnu.org/s/hello/manual/gnulib/arpa_002finet_002eh.html

You can see that mingw and mingw-w64 don't provide those headers. Not sure what to do about netinet/ip.h, though.