[CMake] Parallel builds do not work correctly when using "cmake -E copy" to copy files

[Bryan O'Sullivan]

Alan W. Irwin wrote:

> It was good to hear that make -j N normally works with CMake.

Yes indeed.  I frequently run make -j70 across a 35-host dual-CPU
cluster using distcc, and every time I've updated CMake's files, it's
correctly rebuilt the makefiles before continuing.

	<b