[CMake] Supporting languages where compilation of one file produces multiple files

[Jack Kelly]

Hi all,

I'm specifically thinking about OCaml here, but the problem generalises 
to other languages where the compiler doesn't output exactly one file. 
If I compile a .ml file using the native code compiler:

$ ocamlopt -c -o foo.cmx foo.ml

It will also produce a .o file and possibly a .cmi file (if an explicit 
interface file foo.mli was not present)

I guess the rule for CMAKE_OCaml_COMPILE_OBJECT would be
"<CMAKE_OCaml_COMPILER> <FLAGS> -c -o <OBJECT> <SOURCE>"
but there doesn't seem to be any way to store that these extra files 
have been generated.

-- Jack