target/m68k: implement opcode fetoxm1

target/m68k: implement opcode fetoxm1

Example provided in the launchpad bug fails with:

   qemu: uncaught target signal 4 (Illegal instruction) - core dumped
   Illegal instruction (core dumped)

It appears fetoxm1 is not implemented:

   IN: expm1f
   0x800005cc: fetoxm1x %fp2,%fp0
   Disassembler disagrees with translator over instruction decoding
   Please report this to qemu-devel@nongnu.org

   (gdb) x/2hx 0x800005cc
   0x800005cc: 0xf200 0x0808

This patch adds the instruction.

Bug: https://bugs.launchpad.net/qemu/+bug/1881450
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200531131951.631902-1-laurent@vivier.eu>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>