Create Mach-o files with mode 0777 to allow executing them.

Create Mach-o files with mode 0777 to allow executing them.

Until now, I was always doing chmod +x before running my files on the
Mac.  Now files get created +x.  There's no change when overwriting
an existing file.  I needed to gmake clean my build to remove the
example programs without +x, so cvmach can create them with +x.