The new ARCH=x86 kernel build causes weired machine strings on 32-bit.
For a cross-compiled kernel I have
$ uname -m
x66_64
For a kernel natively built on a 32 bit machine I have
$ uname -m x66
Looking at the sources, I think that utsname->machine was initially
set as "x86_64" and "x86", respectively.
But in arch/x86/kernel/cpu/bugs.c in check_bugs() the second character
is set to '6' on my K7.
I think the right solution for that problem is to use "x86_64" as the
machine name for 64-bit and to keep the old "i[3456]86" strings for
32-bit kernels.