[WIP] Update the cmake find modules to follow FindGMP.cmake

Updated modules do not follow `FindGMP.cmake` exactly. I avoided using `"${MODULE_DIR}/include"` and `"${MODULE_DIR}/lib"` (where `MODULE` is any module name) in `find_path` and `find_library` respectively. Now the find modules look more like `FindBFD.cmake`. I guess the variable `$MODULE_DIR` is not defined for most of the modules. So why do we have it in `find_path` and `find_library`? 

@certik: I just want to know your opinion on this. I'll polish things up after your feedback.