mips.c (function_arg_pass_by_reference): Force to 0 in o32 and o64 ABIs.

mips.c (function_arg_pass_by_reference): Force to 0 in o32 and o64 ABIs.

* config/mips/mips.c (function_arg_pass_by_reference): Force to 0
in o32 and o64 ABIs.
* config/mips/abi64.h (MUST_PASS_IN_STACK): Define as in expr.h,
but getting fixed-size structs passed in registers regardless of
padding in o32 and o64 ABIs.

From-SVN: r50480