Fix packaging for clang, lldb and lld 3.9.0

[dim]

Summary

During the upgrade of clang/llvm etc to 3.9.0 in rS309124, the PACKAGE
directive in the usr.bin/clang/*.mk files got dropped accidentally.

Here is an attempt to restore it, with a few minor additions:

• Correct license in clang.ucl to NCSA (unsure if this breaks anything)
• Add PACKAGE=clang for clang and most of the "ll" tools
• Put lldb in its own package (unsure if such granularity is desired)
• Put lld in its own package (unsure if such granularity is desired)