Fix packaging for clang, lldb and lld 3.9.0

During the upgrade of clang/llvm etc to 3.9.0 in r309124, the PACKAGE
directive in the usr.bin/clang/*.mk files got dropped accidentally.

Restore it, with a few minor changes and additions:

• Correct license in clang.ucl to NCSA
• Add PACKAGE=clang for clang and most of the "ll" tools
• Put lldb in its own package
• Put lld in its own package

Reviewed by: gjb, jmallett
X-MFC-With: 309124
Differential Revision: https://reviews.freebsd.org/D8666