Switched from using diff to cmp for two reasons:

Switched from using diff to cmp for two reasons:
	o Not all versions of diff have the -q option
	o The cmp program is probably faster than diff
Fixed the logic that only copies the file over if no differences are found.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7615 91177308-0d34-0410-b5e6-96231b3b80d8