GPT vs MBR for swap devices

[Trev]

I gave in and bought an Raspberry Pi 3B+ and now I've been bitten by 
Bob's OOM assassin too...

  % gpart show
=>      63  31116225  mmcsd0  MBR  (15G)
         63      2016          - free -  (1.0M)
       2079    102312       1  fat32lba  [active]  (50M)
     104391  31008825       2  freebsd  (15G)
   31113216      3072          - free -  (1.5M)

=>       0  31008825  mmcsd0s2  BSD  (15G)
          0        57            - free -  (29K)
         57  31008768         1  freebsd-ufs  (15G)

=>      40  60567472  da0  GPT  (29G)
         40   4194304    1  freebsd-swap  (2.0G)
    4194344  56373168    2  freebsd-ufs  (27G)

% cat /etc/fstab
# Custom /etc/fstab for FreeBSD embedded images
/dev/ufs/rootfs   /       ufs     rw,noatime      1       1
/dev/msdosfs/MSDOSBOOT /boot/msdos msdosfs rw,noatime 0 0
md1 /tmp mfs rw,noatime,-s100m 0 0
md2 /var/log mfs rw,noatime,-s15m 0 0
md3 /var/tmp mfs rw,noatime,-s15m 0 0
/dev/ufs/swap   none    swap    sw      0       0
/dev/ufs/usr    /usr    ufs     rw,noatime      2       2

da0 is a brand new 32G EMTEC USB2 memory key housing /usr and swap 
partitions.

FreeBSD 12.0-CURRENT #0 r335317: Mon Jun 18 17:37:04 UTC 2018 
root at releng3.nyi.freebsd.org:/usr/obj/usr/src/arm64.aarch64/sys/GENERIC 
arm64

make -j4 buildworld resulted in:

Jun 21 17:05:12 rpi3 kernel: pid 10326 (c++), uid 0, was killed: out of 
swap space
--- CodeGen/AsmPrinter/CodeViewDebug.o ---
c++: error: unable to execute command: Killed
c++: error: clang frontend command failed due to signal (use -v to see 
invocation)
FreeBSD clang version 6.0.0 (tags/RELEASE_600/final 326565) (based on 
LLVM 6.0.0)
Target: aarch64-unknown-freebsd12.0
Thread model: posix
InstalledDir: /usr/bin
c++: note: diagnostic msg: PLEASE submit a bug report to 
https://bugs.freebsd.org/submit/ and include the crash backtrace, 
preprocessed source, and associated run script.
c++: note: diagnostic msg:

I happened to have been watching top (5 second interval) at the time and 
of the 2G swap, only 45M was shown to be in use.