reproducible crash when building sysutils/net-snmp

["Steven M. Bellovin" <smb%cs.columbia.edu@localhost>]

I'm trying to rebuild sysutils/net-snmp on a T61 running
amd64-current.  The disk is FFS; I'm not using softdep.  Every time I
try the build, the system hangs or panics.  This last time, I turned
off cpu1; it didn't help.  The kernel is from last night.  Here's the
backtrace from the dump:

#0  0xffffffff80503105 in cpu_reboot (howto=256, bootstr=<value optimized out>)
    at /usr/src/sys/arch/amd64/amd64/machdep.c:666
666                     dumpsys();
(gdb) bt
#0  0xffffffff80503105 in cpu_reboot (howto=256, bootstr=<value optimized out>)
    at /usr/src/sys/arch/amd64/amd64/machdep.c:666
#1  0xffffffff80463178 in panic (
    fmt=0xffffffff80961f05 <Address 0xffffffff80961f05 out of bounds>)
    at /usr/src/sys/kern/subr_prf.c:230
#2  0xffffffff80504e94 in trap (frame=0xffff80004f3428b0)
    at /usr/src/sys/arch/amd64/amd64/trap.c:264
#3  0xffffffff80100f02 in calltrap ()
#4  0x0000000000001000 in ?? ()
Previous frame inner to this frame (corrupt stack?)

I was able to rebuilt most of my other packages without any trouble;
however, the system also crashed while I was deleting all of my packages
prior to doing the rebuild.