Allow unregisterised ghc-8.4 to build newer GHC

Allow unregisterised ghc-8.4 to build newer GHC

Commit 4075656e8bb introduced a regression stopping existing unregisteristed
compilers from being able to compile newer versions of GHC. The problem is
that the bootstrap compiler uses the newer `rts/storage/ClosureTypes.h` file
where some defines have been renamed, resulting in the following error:
.
  error: ‘stg_MUT_ARR_PTRS_FROZEN0_info’ undeclared (first use in this function); did you mean ‘stg_MUT_ARR_PTRS_FROZEN_DIRTY_info’?
.
 For more information, see https://gitlab.haskell.org/ghc/ghc/issues/15913.
.
 This patch can be removed, once ghc-8.4 is no longer the bootstrap compiler.
Author: Ilias Tsitsimpis <iliastsi@debian.org>
Bug: https://gitlab.haskell.org/ghc/ghc/issues/15913
Bug-Debian: https://bugs.debian.org/932941

Gbp-Pq: Name fix-build-using-unregisterized-v8.4