[CMake] COMPILE_FLAGS suggestion

[Brad King]

Brandon J. Van Every wrote:
> Since you 
> only implemented per-target flags recently, your perception is probably 
> that it's uncommon.  Instead you're probably thinking that everyone 
> makes *.h files and subdirectories.

In CMake's earliest days it was part of a project that had one library 
per directory.  That is why things seem to be directory-based.  Recently 
we've been trying to shift things to be target oriented instead of 
directory oriented.  The entire new Makefile generator added in CMake 
2.2 was written for this purpose.

As things become more target oriented the SET_TARGET_PROPERTIES command 
will be used more frequently.  Eventually a nicer interface should be 
available to set these properties but that interface will be determined 
on a per-property basis.  I just don't want to jump the gun and add a 
bunch of commands that turn out not to be the best interface and then 
have to be supported for compatibility.  For now individual projects can 
use macros to make things look like what they want.

-Brad