[lldb] Silence unhandled enums warning.

The warning was introduced by r346392, which introduces new builtin
types (to support cl_intel_device_side_avc_motion_estimation OpenCL
extension).

Note that this patch only inserts empty cases to silence the warning and
unblock our integrate, does not aim to add support for the new types in
lldb.

llvm-svn: 346441