config.mak.uname: Cygwin needs OBJECT_CREATION_USES_RENAMES

config.mak.uname: Cygwin needs OBJECT_CREATION_USES_RENAMES

This is necessary to use Git on Windows shared directories, and is
already enabled for the MinGW and plain Windows builds.

This problem was reported on the Cygwin mailing list at
https://cygwin.com/ml/cygwin/2015-08/msg00102.html (amongst others)
and is being applied as a manual patch to the Cygwin builds until
the patch is taken here.

Reported-by: Peter Rosin <peda@lysator.liu.se>
Signed-off-by: Adam Dinwoodie <adam@dinwoodie.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>