MIPS/BFD: Correctly handle `bfd_reloc_outofrange' with branches

MIPS/BFD: Correctly handle `bfd_reloc_outofrange' with branches

Fix internal errors like:

ld: BFD (GNU Binutils) 2.26.51.20160526 internal error, aborting at .../bfd/elfxx-mips.c:10278 in _bfd_mips_elf_relocate_section

ld: Please report this bug.

triggered by the `bfd_reloc_outofrange' condition on branch relocations.

	bfd/
	* elfxx-mips.c (b_reloc_p): New function.
	(_bfd_mips_elf_relocate_section) <bfd_reloc_outofrange>: Handle
	branch relocations.

	ld/
	* testsuite/ld-mips-elf/unaligned-branch.d: New test.
	* testsuite/ld-mips-elf/unaligned-branch.s: New test source.
	* testsuite/ld-mips-elf/unaligned-text.s: New test source.
	* testsuite/ld-mips-elf/mips-elf.exp: Run the new test.