Fix build evidence for DF-2839:

The full `make -j6 nativekernel && make installkernel` log lived in the
guest's /tmp and was lost at the reboot into the patched kernel (my
oversight). Substituted evidence that the build ran and booted:

  - uname on the patched guest:
    DragonFly dfbsd 6.5-DEVELOPMENT #1: Wed Sep  2 05:47:01 UTC 2026
    root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC  x86_64
    (stock snapshot kernel was #0: Thu Jul  2 06:02:54 UTC 2026)
  - /boot/kernel/kernel mtime Sep  2 05:50 (fresh install), size 119340592
  - the one-line patch applied cleanly before the build:
    `patch -p1 < fix.diff` -> "Hunk #1 succeeded at 682." on
    sys/kern/kern_exit.c
  - behavioral proof on the patched kernel is fix.run.log:
    upmap 37/148K before and after two 45s race runs (96.6K allocation
    requests served, zero net growth), vs +~7,000 allocations per run on
    the stock kernel.