COMPILING_BASE_PACKAGE macro should be COMPILING_GHC_INTERNAL_MACRO

The COMPILING_BASE_PACKAGE macro is concerned with issues defining symbols and using symbols in the same compilation unit. However, these symbols now exist in ghc-internal rather than base, so we should rename the macro accordingly.

The code is guards is likely never used as we never produce windows DLLs but it is simpler to just perform the renaming for now.