After upgrading my MinGW installation, TyrQuake started to crash in a very
strange way. Eventually, tracked it down to gcc's unit-at-a-time
optimisation. This patch disables unit-at-a-time for gcc earlier than
4.0. (Current MinGW is 3.4.5). Version checking script shamelessly stolen from
Linux.
Signed-off-by: Tyrann <tyrann@disenchant.net>
