Committed, PR target/85666

[Hans-Peter Nilsson]

I've back-ported these two patches to the gcc-8-branch to
restore buildability.  Tested at r264184, committed r264351.

        PR target/85666
        * config/mmix/mmix.c (mmix_assemble_integer): Handle byte-size
        non-CONST_INT rtx:es using assemble_integer_with_op ".byte".
        (MMIX_CFUN_NEEDS_SAVED_EH_RETURN_ADDRESS): Don't call
        leaf_function_p, instead use has_hard_reg_initial_val.

brgds, H-P