* config/mips/abi.h: Use ABI_O64, duplicating ABI_32 usage.
	* config/mips/iris6.h: Same.
	* config/mips/mips.md: Same.
	* config/mips/mips.c: Same; also add "-mabi=o64" option.
	* config/mips/mips.h: Same; also define ABI_O64.

From-SVN: r23809