How to compile kernel for i686 instead of i386?

[Mayuresh <mayuresh%acm.org@localhost>]

The `machine' command prints i386 on my machine, which is the architecture
for which the kernel gets compiled, even though the processor is i686
based.

Is it possible to compile the NetBSD kernel for i686 architecture instead
of i386?

I do not know what it will improve for me. But the expectation is it might
improve performance.

Mayuresh