Add a debug info code generation level to the compile unit metadata
and update everything accordingly. This can be used to conditionalize
the amount of output in the backend based on the amount of debug
requested/metadata emission scheme by a front end (e.g. clang).

Paired with a commit to clang.
If we're only emitting line tables for a particular CU then don't add
any ranges to the list of ranges for the CU as we don't want to emit
them anyway. This ensures that we will still emit ranges if we have
a compile unit compiled with only line tables and one compiled with
full debug info requested (we'll emit for the one with full debug info).

Update testcase metadata accordingly to continue emitting ranges.
Pass down the debug emission kind into the compile unit for code
generation purposes.
Paired with a commit to llvm.