DF-2879 fix kernel build (in-guest, verbatim decisive lines from the session capture;
/tmp/kbuild.log was wiped by the post-install reboot, the full log below is the
tail captured live plus the completion banner)

Commands (as root in guest):
  cd /usr/src && patch -p1 < /tmp/fix_2879.diff
  cd /usr/src && make -j6 nativekernel KERNCONF=X86_64_GENERIC
  cd /usr/src && make installkernel KERNCONF=X86_64_GENERIC

patch output:
  Patching file sys/vm/vm_swap.c using Plan A...
  Hunk #1 succeeded at 362.
  done
  377:	aligned_nblks = (swblk_t)nblks;

make nativekernel (tail, live capture):
  --- libiconv.ko ---
  cc -Wl,--build-id=sha1 -nostdlib -Wl,--hash-style=sysv -r -Wl,-d -o libiconv.ko iconv.o iconv_ucs.o iconv_xlat.o iconv_xlat16.o iconv_converter_if.o
  <=== libiconv
  --------------------------------------------------------------
  >>> Kernel build for X86_64_GENERIC completed on Wed Sep  2 20:46:41 UTC 2026
  --------------------------------------------------------------
  rc=0
  error-count (grep -c "error:"): 0

make installkernel:
  >>> Kernel install for X86_64_GENERIC completed on Wed Sep  2 20:53:07 UTC 2026
  --------------------------------------------------------------
  -r-xr-xr-x  1 root  wheel  119340416 Sep  2 20:52 /boot/kernel/kernel

booted patched kernel:
  DragonFly 6.5-DEVELOPMENT #1: Wed Sep  2 20:43:17 UTC 2026  root@dfbsd:/usr/obj/usr/src/sys/X86_64_GENERIC