This patch adds support for more relocations in relocatable link.  It also
introduces get_lo16_rel_addend method for finding partnering LO16 relocation
because there is a problem with current implementation when using --threads
option.

Regards,
Vladimir

ChangeLog -

	PR gold/21152
	* target.h (Sized_target::relocate_special_relocatable): Add
	reloc_count parameter.
	* arm.cc (Target_arm::relocate_special_relocatable): Likewise.
	* target-reloc.h (relocate_relocs): Pass reloc_count to
	relocate_special_relocatable.
	* mips.cc (Mips_scan_relocatable_relocs::local_section_strategy):
	Return RELOC_SPECIAL for more relocations.
	(Symbol_visitor_check_symbols::operator()): Check for is_output_pic
	rather then checking output_is_position_independent option.
	(Target_mips::is_output_pic): New method.
	(Mips_relocate_functions::get_lo16_rel_addend): Likewise.
	(Target_mips::set_gp): Add case for relocatable link.
	(Target_mips::relocate_special_relocatable): Add reloc_count
	parameter.  Add support for RELA type of relocation sections.
	Add support for more relocations.  Remove unused code.