Log Message:
ghc98: Incredibly ugly workaround to fix Darwin.

Ultimately, the problem here is that GHC goes looking for things in places it
should not be.  If libiconv is installed, it ends up trying to link against the
pkgsrc libiconv, even if it is not buildlinked.  The problem is that the
bootstrap kits are built with native libiconv, and so this breaks the build as
they are looking for iconv_*() vs pkgsrc libiconv which uses libiconv_*().

Unfortunately setting PREFER.iconv=native isn't enough.  For some reason gtar
is being pulled in as a tool, and because of nls that ends up pulling in
gettext-lib and therefore libiconv, which still breaks the build.  The native
tar works fine on Darwin, so we also need to add an exclusion to avoid gtar
being added to USE_TOOLS.

This "fix" will only really work in bulk builds.  As soon as libiconv is
installed via any other dependency it's game over.