Project:LLVM/LLVM 10 packaging changes

Starting with LLVM 10, Gentoo is switching back to the 'dylib' model recommended by upstream, and removing split shared (and static) libraries.

no longer provides split libLLVM*. Applications should simply link to -lLLVM.

no longer provides split libclang*. C++ application should link to -lclang-cpp. Additionally, -lclang is provided as before.

no longer installs any libraries. This might change if there's a need to expose its API in the future.

no longer provides split liblldb*. Its API is provided as -llldb.