Unfortunately, it looks like
/Library/Frameworks/GHC.framework/Versions/7.4.2-x86_64/usr/lib/ghc-7.4.2/libffi.dylib
is pointing to the dodgy library too, e.g.:
> otool -L /Library/Frameworks/GHC.framework/Versions/7.4.2-x86_64/usr/lib/ghc-7.4.2/libffi.dylib
/Users/ian/zz64/ghc-7.4.2/libffi/build/inst/lib/libffi.5.dylib (compatibility version 6.0.0, current version 6.10.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 159.1.0)
Not sure what to patch the first reference in that one to.