* target-reloc.h (class Default_comdat_behavior): New, package up..

	* target-reloc.h (class Default_comdat_behavior): New, package up..
	(get_comdat_behaviour): ..this.
	(relocate_section): Add Relocate_comdat_behavior template arg,
	adjust code to suit.
	* arm.cc (Target_arm::relocate_section): Adjust to suit.
	(Target_arm::scan_reloc_section): Likewise.
	* i386.cc (Target_i386::relocate_section): Likewise.
	* sparc.cc (Target_sparc::relocate_section): Likewise.
	* tilegx.cc (Target_tilegx::relocate_section): Likewise.
	* x86_64.cc (Target_x86_64::relocate_section): Likewise.
	* powerpc.cc (class Relocate_comdat_behavior): New.
	(Target_powerpc::relocate_section): Don't zap opd relocs.  Supply
	gold::relocate_section with new template arg.