Add clang-tools-extra, lld and lldb to the scripts

The scripts aren't very consistent about which repos they handle (e.g.
clang-tools-extra was handled in llvm-prepare, but not in the other scripts).
This commit tries to improve on that by:
* adding support for clang-tools-extra in llvm-projs, llvm-sync and llvm-branch
* adding support for lld and lldb to llvm-branch.

Change-Id: I82b0aeb95b5116d1d75f0721e0c4d31c4744e04b
4 files changed