i386 9.99.17 build fails for NET4501 kernel

["John D. Baker" <jdbaker%consolidated.net@localhost>]

Building the NET4501 kernel with 9.99.17 sources fails with:

[...]
#   compile  NET4501/vm_machdep.o
/r0/build/current/tools/amd64/bin/i486--netbsdelf-gcc -msoft-float -mno-mmx -mno-sse -mno-avx -ffreestanding -fno-zero-initialized-in-bss -fno-delete-null-pointer-checks -g -Os -fstack-protector -Wstack-protector --param ssp-buffer-size=1 -fno-strict-aliasing -fno-common -std=gnu99 -Werror -Wall -Wno-main -Wno-format-zero-length -Wpointer-arith -Wmissing-prototypes -Wstrict-prototypes -Wold-style-definition -Wswitch -Wshadow -Wcast-qual -Wwrite-strings -Wno-unreachable-code -Wno-pointer-sign -Wno-attributes -Wextra -Wno-unused-parameter -Wold-style-definition -Wno-sign-compare --sysroot=/r0/build/current/DEST/i386 -Di386 -I. -I/x/current/src/sys/external/bsd/acpica/dist -I/x/current/src/sys/external/bsd/libnv/dist -I/x/current/src/sys/../common/lib/libx86emu -I/x/current/src/sys/../common/lib/libc/misc -I/x/current/src/sys/../common/include -I/x/current/src/sys/arch -I/x/current/src/sys -nostdinc -DCOMPAT_UTILS -DTIMER_FREQ=1189200 -DCOMPAT_44 -D_KERNEL -D_KERNEL_OPT -std=gnu99 -I/x/current/src/sys/lib/libkern/../../../common/lib/libc/quad -I/x/current/src/sys/lib/libkern/../../../common/lib/libc/string -I/x/current/src/sys/lib/libkern/../../../common/lib/libc/arch/i386/string -D_FORTIFY_SOURCE=2 -I/x/current/src/sys/external/isc/atheros_hal/dist -I/x/current/src/sys/external/isc/atheros_hal/ic -I/x/current/src/sys/external/bsd/libnv/dist -c /x/current/src/sys/arch/x86/x86/vm_machdep.c -o vm_machdep.o
/x/current/src/sys/arch/x86/x86/vm_machdep.c: In function 'cpu_lwp_fork':
/x/current/src/sys/arch/x86/x86/vm_machdep.c:134:21: error: variable 'pcb2' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered]
  struct pcb *pcb1, *pcb2;
                     ^~~~
cc1: all warnings being treated as errors
*** [vm_machdep.o] Error code 1

nbmake: stopped in /r0/build/current/obj/i386/sys/arch/i386/compile/NET4501
1 error

nbmake: stopped in /r0/build/current/obj/i386/sys/arch/i386/compile/NET4501

ERROR: Failed to make all in "/r0/build/current/obj/i386/sys/arch/i386/compile/NET4501"
*** BUILD ABORTED ***


-- 
|/"\ John D. Baker, KN5UKS               NetBSD     Darwin/MacOS X
|\ / jdbaker[snail]consolidated[flyspeck]net  OpenBSD            FreeBSD
| X  No HTML/proprietary data in email.   BSD just sits there and works!
|/ \ GPGkeyID:  D703 4A7E 479F 63F8 D3F4  BD99 9572 8F23 E4AD 1645