openbios fails to build with gcc-16 (powerpc code)

Hi!

Since debian switch from gcc-15 to gcc-16, qemu fails to build openbios-powerpc:

powerpc-linux-gnu-gcc -m32 -mcpu=604 ...\
  roms/openbios/arch/ppc/qemu/start.S

roms/openbios/arch/ppc/qemu/start.S:292: Error: unrecognized opcode: `clrldi'
roms/openbios/arch/ppc/qemu/start.S:293: Error: unrecognized opcode: `mtmsrd'
roms/openbios/arch/ppc/qemu/start.S:178: Error: unrecognized opcode: `std'
[a lot of other similar errors]

I know nothing about powerpc assembler.  Google tells me mtmsrd is a 64bit-only
instruction which can't be used in 32bit mode (which is in effect here).

It feels like start.S uses the wrong assembly?  I wonder how it worked before..

Additionally, there's this new error (due to -Werror being in effect),
but it is easy to deal with:

In file included from /build/pkg/build/roms/openbios/kernel/bootstrap.c:28:
roms/openbios/kernel/bootstrap.c: In function ‘write_dictionary’:
roms/openbios/kernel/include/dict.h:12:16: warning: initializer-string for array of ‘char’ truncates NUL terminator but destination lacks ‘nonstring’ 
attribute (9 chars into 8 available) [-Wunterminated-string-initialization]
    12 | #define DICTID "OpenBIOS"
       |                ^~~~~~~~~~
roms/openbios/kernel/bootstrap.c:170:35: note: in expansion of macro ‘DICTID’
   170 |                 .signature      = DICTID,
       |                                   ^~~~~~


FWIW,

/mjt