Cabal reports mismatched interface file ways dyn

[Stefan Schulze Frielinghaus]

I'm resurrecting an old thread because I thought that this might also be
helpful for others. The problem I encountered was a result of old build
artifacts which didn't get cleaned up.

Assume you have build GHC before and now you changed something e.g. the
LLVM compiler. Thus the build system won't detect automatically that you
have to recompile and therefore you want to go for a full build by doing
a clean in the first place.

$ make maintainer-clean
$ git status --ignored
...
Ignored files:
    libraries/ghc-heap/dist-boot
...

The maintainer-clean target does not remove all build artifacts. Thus it
is more save to perform a `git clean -dfx`. In my case this solved the
problem.

Cheers,
Stefan