[arch-dev-public] LLVM 6 and splitting up {clang, lld, lldb, compiler-rt} into separate PKGBUILDs

[Evangelos Foutras]

I pushed llvm 6.0.0-1 to [staging] without the rest of the packages
mentioned in the subject. I am planning to add them back as individual
packages in the following days.

This separation will bring faster builds when one of these components needs
patching. It also allows building clang with shared libraries and merging
the extra-tools package into it (thus fixing https://bugs.archlinux.org/tas
k/50865).

Once everything is in [staging], I'll create a TODO list for rebuilds as
usual.