Fixed compilation on recent version of cygwin.

git-svn-id: http://svn.aircrack-ng.org/trunk@2340 28c6078b-6c39-48e3-add9-af49d547ecab
Cygwin: gcc-4 doesn't exist anymore, it's just gcc.

git-svn-id: http://svn.aircrack-ng.org/trunk@2341 28c6078b-6c39-48e3-add9-af49d547ecab