Problems building world on 313159

[bob prohaska]

For the last couple of days buildworld has been stopping with the error

/usr/src/sys/boot/efi/libefi/env.c:97:50: error: format specifies type 'unsigned long' but the argument has type 'EFI_STATUS' (aka 'unsigned int') [-Werror,-Wformat]
                printf("Can't get the variable: error %#lx\n", status);
                                                      ~~~~     ^~~~~~
                                                      %#x
The sources are at 313159, the building system is at r312991. The first 
time it failed I ran a make clean, the second time I removed /usr/obj/usr,
each time updating sources between tries.

This is self-hosted on an RPI2, but the error looks hardware-independent
to me. Absence of prior discussion  suggests some  local mistake.
No intentional changes have been made for over a month, so I'm stumped.

Thanks for reading, any suggestions appreciated.

bob prohaska