* Renounce to dynamically construct download URL.
The download link is now defined as a cookbook attribute, since
llvm.org packages do not follow stable naming conventions.
* Use 'ark' resource to download and install clang tarball.
> The llvm-ld tool has been removed. The clang driver provides a
> more reliable solution for turning a set of bitcode files into a
> binary. To merge bitcode files llvm-link can be used instead.
This cookbook is not (yet) oriented to install "all possible" clang versions.
If wanting to do so, the list of binaries to symlink should be
dynamically constructed based on clang version, or extracted as cookbook
attribute to give more flexibility.