[lldb-instr] Don't print REGISTER macro when RECORD is already present

Currently we'd always print the LLDB_REGISTER macro, even if the
LLDB_RECORD macro was already present. This patches changes that to make
it easier to incrementally update the macros.

Note that it's still possible for the RECORD and REGISTER macros to get
out of sync.

llvm-svn: 354400