If you add a module to GHC, I know you need to extend ghc.cabal.in.   But also ghc.mk? Otherwise I get hits

If you add a module to GHC, I know you need to extend ghc.cabal.in.   But also ghc.mk? Otherwise I get hits
/usr/bin/ar: creating rts/dist/build/libHSrts_debug.a

Reachable modules from DynFlags out of date

Please fix compiler/ghc.mk, or building DLLs on Windows may break (#7780)

Extra modules: CoreOpt

make[1]: *** [compiler/stage2/dll-split.stamp] Error 1

make[1]: *** Waiting for unfinished jobs....

make: *** [all] Error 2

Is it necessary to have two places to extend?

Simon