kern/53399: Assert failure in ch_voltag_convert_in called from fpu_eagerswitch()

[phil%netbsd.org@localhost]

>Number:         53399
>Category:       kern
>Synopsis:       Assert failure in ch_voltag_convert_in called from fpu_eagerswitch()
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jun 26 18:10:00 +0000 2018
>Originator:     Phil Nelson
>Release:        8.99.20
>Organization:
>Environment:
NetBSD steelhead.pcnelson.net 8.99.20 NetBSD 8.99.20 (STEELHEAD) #1: Tue Jun 26 09:29:27 PDT 2018  phil%steelhead.pcnelson.net@localhost:/home/phil/netbsd/src/sys/arch/amd64/compile/STEELHEAD amd64

Machines is a Dell optiplex 3020, quad core Intel(R) Core(TM) i5-4590, 8GB of memory
>Description:
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] panic: kernel diagnostic assertion "pcb->pcb_fpcpu == NULL" failed: file "/usr/src/sys/arch/x86/x86/fpu.c", line 345 
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] cpu2: Begin traceback...
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] vpanic() at netbsd:vpanic+0x16f
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] ch_voltag_convert_in() at netbsd:ch_voltag_convert_in
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] fpu_eagerswitch() at netbsd:fpu_eagerswitch+0xd5
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] cpu_switchto() at netbsd:cpu_switchto+0x56
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] sleepq_block() at netbsd:sleepq_block+0xaa
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] cv_wait() at netbsd:cv_wait+0xfb
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] fork1() at netbsd:fork1+0x87e
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] sys___vfork14() at netbsd:sys___vfork14+0x2c
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] syscall() at netbsd:syscall+0x208
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] --- syscall (number 282) ---
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] 70da5228adec:
Jun 25 14:57:29 steelhead /netbsd: [ 21411.5077674] cpu2: End traceback...
Jun 25 14:57:42 steelhead savecore: reboot after panic: [ 21411.5077674] panic: kernel diagnostic assertion "pcb->pcb_fpcpu == NULL" failed: file "/usr/src/sys/arch/x86/x86/fpu.c", line 345 

>How-To-Repeat:
I was building packages ... has done this consistently while building packages.
>Fix: