Checkpoint for ECOFF support. Can assemble hello, world.

Checkpoint for ECOFF support.  Can assemble hello, world.

	* config/obj-ecoff.c, config/obj-ecoff.h: Preliminary ECOFF
	support.

	* config/tc-mips.h (TARGET_FORMAT): Define based on OBJ_AOUT vs.
	OBJ_ECOFF as well as TARGET_BYTES_*_ENDIAN.
	(struct loc, struct proc, struct file): Moved to tc-mips.c within
	#ifndef OBJ_ECOFF block, since ECOFF uses different versions.
	* config/tc-mips.c: Rearranged for ECOFF support.  Added
	prototypes for all static functions.  Moved existing minimal
	debugging format support info #ifndef OBJ_ECOFF blocks.
	(macro_build_lui): Eliminated sign_extend argument, because ECOFF
	does not support a non sign extended high 16 bits reloc.  Adjusted
	all callers accordingly.
	(tc_get_register): Renamed from get_register, and made non-static.

	* config/mips-big.mt, config/mips-lit.mt: New files.  Define
	TARGET_BYTES_BIG_ENDIAN and TARGET_BYTES_LITTLE_ENDIAN,
	respectively.
	* configure.in (mips-*-bsd*): Use gas_target mips-lit.
	(mips-*-ultrix*, mips-*-irix*, mips-*-ecoff): New targets, using
	obj_format ecoff and gas_target mips-lit or mips-big.