Dump Cmm with -ddump-cmm when building .cmm files

Fixes #16131

compiler/main/HscMain.hs

@@ -1438,6 +1438,7 @@ hscCompileCmmFile hsc_env filename output_filename = runHsc hsc_env $ do
             mod_name = mkModuleName $ "Cmm$" ++ FilePath.takeFileName filename
             cmm_mod = mkModule (thisPackage dflags) mod_name
         (_, cmmgroup) <- cmmPipeline hsc_env (emptySRT cmm_mod) cmm
+        dumpIfSet_dyn dflags Opt_D_dump_cmm "Output Cmm" (ppr cmmgroup)
         rawCmms <- cmmToRawCmm dflags (Stream.yield cmmgroup)
         _ <- codeOutput dflags cmm_mod output_filename no_loc NoStubs [] []
              rawCmms