[PATCH] Document new LLVM CMake interface and emit warning when using llvm_map_components_to_libraries

[Dan Liew]

Hi Brad,

Whilst writing the documentation for something else in LLVM I noticed
this document

http://llvm.org/docs/Projects.html

I think the "Embedding LLVM in your project" documentation on using
LLVM libraries via CMake belongs in here instead. Do you agree? If so
I'll move the "Embedding LLVM in your project" docs (including the
"Developing LLVM Pass out of source") into Project.rst.

I was also thinking of mentioning in the docs that libraries come out
of  llvm_map_components_to_libnames() are imported targets so their
properties can be read.

I've not heard anything from Takumi so I might just go ahead and

- merge these (once the docs are rewritten) into trunk and release_35
- Add a note to the LLVM 3.5 release notes that
llvm_map_components_to_libraries is deprecated and
llvm_map_components_to_libnames
  should be used instead.

Any objections?

Thanks,
Dan.