tune-i686: Add new tune for better support of 686-class CPUs.
There isn't currently any tune available for i686 x86 optimizations.
The tune for i586 doesn't enable i686 specific optimizations, and the
one for core2 enables things that won't work on a i686 CPU (like SSE3).
Make the tune for core2 inherits from this one and move there the
setting of X86ARCH32.
Signed-off-by: Carlos Alberto Lopez Perez <clopez@igalia.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
