ghc-heap: Stack.cmm and Stack.c clash when building with Cabal

Summary

When built with Cabal libraries/ghc-heap/cbits/Stack.c and libraries/ghc-heap/cbits/Stack.cmm clash (the object files for both are written to dist/build/cbits/Stack.o).

@hsyl20 mentioned that apparently hadrian puts artifacts in .../build/{c,cmm,s,...}/.... (avoiding the clash of names).

Steps to reproduce

Use a Cabal based builder to build the ghc-heap package.

Possible Fix

Rename one of the files so that Cabal does not try to build both of them as Stack.o.