x86: change OPTIMIZE_INLINING help to say enabling makes smaller kernels

Impact: clarify Kconfig help text

The OPTIMIZE_INLINING help currently says "The gcc 4.x series have a
rewritten inlining algorithm and disabling this option will generate a
smaller kernel there."

This contradicts other parts of the help text and my own tests:

  5463127 2008-10-11 19:51 vmlinux.no-opt
  5456152 2008-10-11 19:56 vmlinux.opt

Reword text to say that enabling OPTIMIZE_INLINING will lead to smaller
kernels with gcc 4.x or later.

Signed-off-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>