Adds a CMake package configuration file for libclang, so that library users from CMake based project can configure their dependency to libclang easily.

Signed-off-by: Damien Buhl (alias daminetreg) <damien.buhl@lecbna.org>
As adviced by Brad King (CMake maintainer) it's better to use lib/ as folder for package configuration, instead of share/ because it enables arch-specific information to be stored with, as lib/ can be arch specific on linux.
Changed LIBCLANG_LIBRARY_VERSION to also include CINDEX_VERSION_MAJOR and CINDEX_VERSION_MAJOR as they define the libclang API/ABI.