config.gcc (i[34567]86-*-rdos*, [...]): New targets.

	* config.gcc (i[34567]86-*-rdos*, x86_64-*-rdos*): New targets.
	* config/i386/i386.h (TARGET_RDOS): New macro.
	(DEFAULT_LARGE_SECTION_THRESHOLD): New macro.
	* config/i386/i386.c (ix86_option_override_internal): For 64bit
	TARGET_RDOS, set ix86_cmodel to CM_MEDIUM_PIC and flag_pic to 1.
	* config/i386/i386.opt (mlarge-data-threshold): Initialize to
	DEFAULT_LARGE_SECTION_THRESHOLD.
	* config/i386/i386.md (R14_REG, R15_REG): New constants.
	* config/i386/rdos.h: New file.
	* config/i386/rdos64.h: New file.

From-SVN: r195516