rs6000.md (floatsidf2_loadaddr): rs6000_fpmem_offset will be negative in a stackless frame.

        * rs6000.md (floatsidf2_loadaddr): rs6000_fpmem_offset will be
        negative in a stackless frame.
        * rs6000.c (rs6000_stack_info): Don't include fixed-size link area
        in stackless frame size.  Support 64-bit stackless frame size.
        Combine fpmem offset calculations and don't add total_size to
        offset if not pushing a stack frame.

From-SVN: r19283