Revert "[lldb][cmake] Remove libclang as an lldbBase dependency (NFCI)"

This reverts commit r279296. Including LLDBDependencies breaks the
netbsd lldb bot because it exposes LLDB_USED_LIBS, which causes
lldb_link_common_libs to run to completion in unintended sites, which
results in a malformed call to target_link_libraries.

  http://lab.llvm.org:8011/builders/lldb-amd64-ninja-netbsd7/builds/5989

Thanks to Chris Bieneman for figuring this out!

llvm-svn: 279322