Relying on CallStack being in GLASGOW_HASKELL >= 710 breaks
bootstrappability with 7.10.1

7.10.2 added the CallStack mechanism, and GHC already relies on this
while being built. Unfortunately, it is enabled with "GLASGOW_HASKELL
>= 710", which also applies to GHC 7.10.1, which does not have
CallStack, and fails building the stage-1 compiler because the symbol
is not found.

This patch makes the CPP directive more strict, requiring **more than**
7.10 instead of **at least**.

Reviewers: jstolarek, austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1472

GHC Trac Issues: #11085