macho debug changes

This patch is aimed at fixing "FAIL: eqv involving dot" and any
similar problems in real code when generating DWARF.

	* config/obj-macho.c (obj_mach_o_frob_label),
	(obj_mach_o_frob_symbol): Ignore more debug symbols.
	(obj_mach_o_set_subsections): Ignore SEC_DEBUGGING sections.
	(obj_mach_o_force_reloc_sub_same),
	(obj_mach_o_force_reloc_sub_local),
	(obj_mach_o_force_reloc): Add seg param.  Return false when
	processing debug sections.
	* config/obj-macho.h: Update prototypes.
	* config/tc-i386.h <OBJ_MACHO>: Smuggle section being
	processed by TC_FORCE_RELOCATION* to obj_macho_o functions.