gcc: Backport patch to resolve i*86 tune configuration overrides

Upstream has merged a change to handle detection of target overrides so
that they are only applied as required. Backport this patch from
upstream and remove the OE specific patch.

Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>