strange buildworld issue on RELENG_12

I have a number of RELENG_12 boxes I track via svn and git but on one
cannot build a kernel for some reason. I blew away /usr/obj and checked
out a fresh copy of the tree, but buildkernel still fails with

....
--------------------------------------------------------------
>>> stage 3.1: building everything
--------------------------------------------------------------
cd /usr/obj/usr/src/amd64.amd64/sys/GENERIC; MACHINE_ARCH=amd64
MACHINE=amd64 CPUTYPE= CC="cc -target x86_64-unknown-freebsd12.2
--sysroot=/usr/obj/usr/src/amd64.amd64/tmp
-B/usr/obj/usr/src/amd64.amd64/tmp/usr/bin" CXX="c++  -target
x86_64-unknown-freebsd12.2 --sysroot=/usr/obj/usr/src/amd64.amd64/tmp
-B/usr/obj/usr/src/amd64.amd64/tmp/usr/bin" CPP="cpp -target
x86_64-unknown-freebsd12.2 --sysroot=/usr/obj/usr/src/amd64.amd64/tmp
-B/usr/obj/usr/src/amd64.amd64/tmp/usr/bin" AS="as" AR="ar" LD="ld"
LLVM_LINK="" NM=nm OBJCOPY="objcopy" RANLIB=ranlib STRINGS= SIZE="size"
INSTALL="sh /usr/src/tools/install.sh"
PATH=/usr/obj/usr/src/amd64.amd64/tmp/legacy/usr/sbin:/usr/obj/usr/src/amd64.amd64/tmp/legacy/usr/bin:/usr/obj/usr/src/amd64.amd64/tmp/legacy/bin:/usr/obj/usr/src/amd64.amd64/tmp/usr/sbin:/usr/obj/usr/src/amd64.amd64/tmp/usr/bin:/sbin:/bin:/usr/sbin:/usr/bin
make  -m /usr/src/share/mk  KERNEL=kernel all -DNO_MODULES_OBJ
machine -> /usr/src/sys/amd64/include
x86 -> /usr/src/sys/x86/include
cc -target x86_64-unknown-freebsd12.2
--sysroot=/usr/obj/usr/src/amd64.amd64/tmp
-B/usr/obj/usr/src/amd64.amd64/tmp/usr/bin -c -O2 -pipe
-fno-strict-aliasing -g -nostdinc -I. -I/usr/src/sys
-I/usr/src/sys/contrib/ck/include -I/usr/src/sys/contrib/libfdt
-D_KERNEL -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h
-fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -MD
-MF.depend.genoffset.o -MTgenoffset.o
-fdebug-prefix-map=./machine=/usr/src/sys/amd64/include
-fdebug-prefix-map=./x86=/usr/src/sys/x86/include -mcmodel=kernel
-mno-red-zone -mno-mmx -mno-sse -msoft-float
-fno-asynchronous-unwind-tables -ffreestanding -fwrapv -fstack-protector
-gdwarf-2 -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes
-Wmissing-prototypes -Wpointer-arith -Wcast-qual -Wundef
-Wno-pointer-sign -D__printf__=__freebsd_kprintf__
-Wmissing-include-dirs -fdiagnostics-show-option -Wno-unknown-pragmas
-Wno-error=tautological-compare -Wno-error=empty-body
-Wno-error=parentheses-equality -Wno-error=unused-function
-Wno-error=pointer-sign -Wno-error=shift-negative-value
-Wno-address-of-packed-member -Wno-format-zero-length -mno-aes -mno-avx
-std=iso9899:1999 -fcommon /usr/src/sys/kern/genoffset.c
NM='nm' NMFLAGS='' sh /usr/src/sys/kern/genoffset.sh genoffset.o >
offset.inc
cc -target x86_64-unknown-freebsd12.2
--sysroot=/usr/obj/usr/src/amd64.amd64/tmp
-B/usr/obj/usr/src/amd64.amd64/tmp/usr/bin -c -O2 -pipe
-fno-strict-aliasing -g -nostdinc -I. -I/usr/src/sys
-I/usr/src/sys/contrib/ck/include -I/usr/src/sys/contrib/libfdt
-D_KERNEL -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h
-fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -MD
-MF.depend.genassym.o -MTgenassym.o
-fdebug-prefix-map=./machine=/usr/src/sys/amd64/include
-fdebug-prefix-map=./x86=/usr/src/sys/x86/include -mcmodel=kernel
-mno-red-zone -mno-mmx -mno-sse -msoft-float
-fno-asynchronous-unwind-tables -ffreestanding -fwrapv -fstack-protector
-gdwarf-2 -Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes
-Wmissing-prototypes -Wpointer-arith -Wcast-qual -Wundef
-Wno-pointer-sign -D__printf__=__freebsd_kprintf__
-Wmissing-include-dirs -fdiagnostics-show-option -Wno-unknown-pragmas
-Wno-error=tautological-compare -Wno-error=empty-body
-Wno-error=parentheses-equality -Wno-error=unused-function
-Wno-error=pointer-sign -Wno-error=shift-negative-value
-Wno-address-of-packed-member -Wno-format-zero-length -mno-aes -mno-avx
-std=iso9899:1999 -fcommon /usr/src/sys/amd64/amd64/genassym.c
In file included from /usr/src/sys/amd64/amd64/genassym.c:44:
In file included from /usr/src/sys/sys/systm.h:130:
In file included from /usr/src/sys/sys/kpilite.h:33:
./offset.inc:13:26: error: array is too large (18446744073709550697
elements)
        u_char  pad_td_epochnest[0xf9 - (0x48c + sizeof(u_int))];
                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
*** Error code 1

Stop.
make[2]: stopped in /usr/obj/usr/src/amd64.amd64/sys/GENERIC
*** Error code 1
*** Error code 1


Any idea what might be going on ? Nothing in make.conf and src.conf

Previous buildworld was from

#0 r370122: Mon Jul 12 09:18:15 EDT 2021

    ---Mike