bfd PR ld/18401
* elfxx-mips.c (bfd_mips_isa_ext_mach): New function: Converts an
ISA value to a bfd machine number.
(bfd_mips_isa_ext): Update the ISA level and revision if
necessary. Use mips_mach_extends_p to decide if the ISA extension
needs to be set.
(_bfd_mips_elf_merge_private_bfd_data): Allow the ISA extension to
be inferred from the ABI setting. Set the ISA level from the
maximum of the incoming and outgoing ISA levels.
tests
* ld-mips-elf/mips-elf-flags.exp: Add more ISA conflict tests.
