Previously, -ddump-cmmz was used to dump out the "Raw Cmm" right
before it gets passed to the backends, as well as all of the
intermediate phases in the new code generator.  Unfortunately,
there are a lot of intermediate phases, which means -ddump-cmmz
takes a very long time with -fnew-codegen for large programs,
even if you're only interested in the final result.

Here we split up -ddump-cmmz into -ddump-cmmz (now exclusively for
the new code generator) and -ddump-raw-cmm (for both code generation
paths.) The old flag was not documented in the manual, so hopefully
not too many people will be surprised by this change.