This adds ABI flags to MIPS/ELF object files.

For bfd:
	* elf32-mips.c (elf_mips_abi_name): New.
	(_bfd_mips_elf_merge_private_bfd_data): Compare EF_MIPS_ABI flags.

For gas:
	* config/tc-mips.c (mips_abi_string): New.
	(md_parse_option,md_longopts): Add mabi.
	(mips_elf_final_processing): Set e_flags based on mabi flag.

For gcc:
	* config/mips/mips.h (GAS_ASM_SPEC): Pass mabi to gas.
	(ABI_GAS_ASM_SPEC,abi_gas_asm_spec): New.
	(EXTRA_SPECS): Added ABI_GAS_ASM_SPEC,abi_gas_asm_spec.

For include/elf:

	* mips.h (EF_MIPS_ABI,E_MIPS_ABI_O32,E_MIPS_ABI_O64,
	E_MIPS_ABI_EABI32,E_MIPS_ABI_EABI64):