Added a new makefile setting that can be set in LLDB makefiles: USE_LIBCPP. This will enable libc++ support.
Improved the makefile "clean" to include deleting all ".d.[0-9]+" files.

Added options to the "lldb/examples/lookup" example and made it build using the LLDB_BUILD_DIR. If this is not set, it will default to "/Applications/Xcode.app/Contents/SharedFrameworks" on Darwin.

Added options to the "lldb/examples/function" example and made it build using the LLDB_BUILD_DIR.