[CMake] One target being built several times during parallel build

[Brad King]

Denis Scherbakov wrote:
> Brad, could you please, ask someone who knows about this problem in detail
> what is this more important feature and why it is not possible
> to fix this bug?

Please report it here:

   http://www.cmake.org/Bug

> Could you suggest, how to prevent users from trying to compile two targets
> at a time? I think this is a MAJOR bug.

Since no one has been motivated enough to address it in the 9 year history
of the project I wouldn't consider it a showstopping bug.  Besides, even
if one tries this the build should still complete successfully...just with
some waste.

-Brad