Update Makefile

Installed latest Cygwin and couldn't run make without removing -ansi flag. 
https://github.com/AGWA/git-crypt/blob/master/Makefile#L2

make -version 4
gcc -v 4.9.0-1
Else I got this problem:
https://cygwin.com/ml/cygwin/2014-01/msg00130.html