Add --with-abi= support to x86_64-*-*

2012-04-02  H.J. Lu  <hongjiu.lu@intel.com>

	* config.gcc: Use i386/biarchx32.h instead of i386/biarch64.h
	for --with-abi={x32|mx32} or --with-multilib-list=mx32.
	(supported_defaults): Add abi for i[34567]86-*-* and x86_64-*-*.

	* config/i386/biarchx32.h: New.

From-SVN: r186099