8024344: PPC64 (part 112): C argument in register AND stack slot. Summary: On PPC, the first 13 floating point arguments to C calls are passed in floating point registers. Also, all but the first 8 arguments are passed on the stack. So there can be floating point arguments that are passed on the stack and in a register. We duplicate the regs datastructure in c_calling_convention() to represent this. Reviewed-by: kvn, cjplummer