rts: Fix #9003 with an annoying hack

The TL;DR is that by adding this, we can distinguish GHC 7.8.3 from
7.8.2, which had a buggy implementation. See the ticket for details.

Signed-off-by: Austin Seipp <austin@well-typed.com>
(cherry picked from commit bd5f3ef6585640f762d96426bb041d79a5038e8e)