Add flag to dump each Cmm pass output to a separate file (#16930)
This patch implements #16930 (closed) which I created after stumbling upon this TODO.
Implementation details:
- add new flag
-ddump-cmm-verbose-by-proc
which would keep the old behaviour of-ddump-cmm-verbose
.-ddump-cmm-verbose
will now write everything to a separate file if used with-ddump-to-file
- update user guide
- add test
TODO: once this is merged, update https://gitlab.haskell.org/ghc/ghc/wikis/commentary/compiler/code-gen/overview