x86: share more options between 32 and 64 bit build

On recommendation from Andi Kleen share a few more options
between 32 and 64 bit builds.
A defconfig build for i386 did not show any difference in
size of text and data.

The additional shared options are:
-Wno-sign-compare
-fno-asynchronous-unwind-tables
-mno-sse
-mno-mmx
-mno-sse2
-mno-3dnow

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>