Michael van Elst suggested "fdisk -g -u" which may work if doesn't
corrupt GPT partitions. I may try it sometime in the near future.
I've been using an old NetBSD-9.1 VM for these things and the version
of fdisk there doesn't seem to support -g option. I'll just upgrade to
NetBSD-10.
The trick seems to be to have MSDOS as the very first partition,
otherwise it may not boot.
Partition table:
0: Primary DOS with 32 bit FAT - LBA (sysid 12)
start 2048, size 262144 (128 MB, Cyls 0-16/113/33)
1: GPT Protective MBR (sysid 238)
start 1, size 2047 (1 MB, Cyls 0/0/2-0/32/32)
PBR is not bootable: Bad magic number (0x0000)
2: <UNUSED>
3: <UNUSED>
No active partition.
