Add support for .MIPS.abiflags and .gnu.attributes sections.

elfcpp/
	* elfcpp.h (SHT_MIPS_ABIFLAGS): New enum constant.
	* mips.h (EF_MIPS_FP64, EF_MIPS_NAN2008): New enum constants for
	processor-specific flags.
	(E_MIPS_MACH_5900): New enum constant for machine variant.
	(AFL_REG_NONE, AFL_REG_32, AFL_REG_64, AFL_REG_128): New enum
	constants.
	(AFL_ASE_DSP, AFL_ASE_DSPR2, AFL_ASE_EVA, AFL_ASE_MCU,
	AFL_ASE_MDMX, AFL_ASE_MIPS3D, AFL_ASE_MT, AFL_ASE_SMARTMIPS,
	AFL_ASE_VIRT, AFL_ASE_MSA, AFL_ASE_MIPS16, AFL_ASE_MICROMIPS,
	AFL_ASE_XPA): Likewise.
	(AFL_EXT_XLR, AFL_EXT_OCTEON2, AFL_EXT_OCTEONP,
	AFL_EXT_LOONGSON_3A, AFL_EXT_OCTEON, AFL_EXT_5900, AFL_EXT_4650,
	AFL_EXT_4010, AFL_EXT_4100, AFL_EXT_3900, AFL_EXT_10000,
	AFL_EXT_SB1, AFL_EXT_4111, AFL_EXT_4120, AFL_EXT_5400,
	AFL_EXT_5500, AFL_EXT_LOONGSON_2E, AFL_EXT_LOONGSON_2F,
	AFL_EXT_OCTEON3): Likewise.
	(Tag_GNU_MIPS_ABI_FP, Tag_GNU_MIPS_ABI_MSA): Likewise.
	(Val_GNU_MIPS_ABI_FP_ANY, Val_GNU_MIPS_ABI_FP_DOUBLE,
	Val_GNU_MIPS_ABI_FP_SINGLE, Val_GNU_MIPS_ABI_FP_SOFT,
	Val_GNU_MIPS_ABI_FP_OLD_64,Val_GNU_MIPS_ABI_FP_XX,
	Val_GNU_MIPS_ABI_FP_64, Val_GNU_MIPS_ABI_FP_64A,
	Val_GNU_MIPS_ABI_FP_NAN2008, Val_GNU_MIPS_ABI_MSA_ANY,
	Val_GNU_MIPS_ABI_MSA_128): Likewise.
	(AFL_FLAGS1_ODDSPREG): New enum constant.
gold/
	* mips.cc (struct Mips_abiflags): New struct.
	(Mips_relobj::Mips_relobj): Initialize attributes_section_data_
	and abiflags_.
	(Mips_relobj::~Mips_relobj): Delete object pointed by
	attributes_section_data_.
	(Mips_relobj::abiflags): New method.
	(Mips_relobj::attributes_section_data): Likewise.
	(Mips_relobj::attributes_section_data_): New data member.
	(Mips_relobj::abiflags_): Likewise.
	(class Mips_output_section_abiflags): New class.
	(Target_mips::Target_mips): Initialize attributes_section_data_,
	abiflags_ and has_abiflags_section_.
	(Target_mips::do_should_include_section): Don't emit input
	.MIPS.abiflags sections to output .MIPS.abiflags.
	(Target_mips::Mips_mach): Add new enum constants.
	(Target_mips::mips_isa_ext_mach): New method.
	(Target_mips::mips_isa_ext): Likewise.
	(Target_mips::update_abiflags_isa): Likewise.
	(Target_mips::infer_abiflags): Likewise.
	(Target_mips::create_abiflags): Likewise.
	(Target_mips::fp_abi_string): Likewise.
	(Target_mips::select_fp_abi): Likewise.
	(Target_mips::merge_obj_attributes): Likewise.
	(Target_mips::merge_obj_abiflags): Likewise.
	(Target_mips::level_rev): Likewise.
	(Target_mips::merge_obj_e_flags): Rename from
	merge_processor_specific_flags. Remove dyn_obj argument,
	call update_abiflags_isa when needed, compare NaN encodings and
	compare FP64 state.
	(Target_mips::add_machine_extensions): Add two machine extensions
	and fix one.
	(Target_mips::attributes_section_data_): New data member.
	(Target_mips::abiflags_): Likewise.
	(Target_mips::has_abiflags_section_): Likewise.
	(Mips_relobj::do_read_symbols): Read .gnu.attributes and
	.MIPS.abiflags sections if they exists.
	(Target_mips::elf_mips_mach): Add E_MIPS_MACH_5900 and
	E_MIPS_MACH_OCTEON3 support.
	(Target_mips::do_adjust_elf_header): Setup EI_ABIVERSION flag.
	(Target_mips::do_finalize_sections): Merge .gnu.attributes and
	.MIPS.abiflags sections from input. Create these sections if
	needed.
	(Target_mips::elf_mips_mach_name): Add E_MIPS_MACH_5900 and
	E_MIPS_MACH_OCTEON3 support, and change strings for
	E_MIPS_MACH_LS2E, E_MIPS_MACH_LS2F and E_MIPS_MACH_LS3A just
	to match bfd.