Disallow gcc versions 3.{0,1}

GCC 3.0 and 3.1 are too old to build a working kernel.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
[ This check got dropped as obsolete when I simplified the gcc header
  inclusion mess in f153b82121b0366fe0e5f9553545cce237335175, but Willy
  Tarreau reports actually having those old versions still..  -Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>