> I pretty much nuke the compile/BLAH directory every single
> time I build a kernel, just to eliminate this.  It is
> definitely cleanly built.

Try turning off "-march=..." optimisation.  Then rebuild
toolchain, only then the kernel.  Bet you have
-march=pentiumpro defined either explicitly in /etc/mk.conf or
through the cpuflags pkg,

-Evgeni