MIPS16: Add R_MIPS16_PC16_S1 branch relocation support

For R_MIPS16_PC16_S1 the calculation is `(sign_extend(A) + S - P) >> 1'
and the usual MIPS16 bit shuffling applies to relocated field handling,
as per the encoding of the branch target in the extended form of the
MIPS16 B, BEQZ, BNEZ, BTEQZ and BTNEZ instructions.

	include/
	* elf/mips.h (R_MIPS16_PC16_S1): New relocation.

	bfd/
	* elf32-mips.c (elf_mips16_howto_table_rel): Add
	R_MIPS16_PC16_S1.
	(mips16_reloc_map): Likewise.
	* elf64-mips.c (mips16_elf64_howto_table_rel): Likewise.
	(mips16_elf64_howto_table_rela): Likewise.
	(mips16_reloc_map): Likewise.
	* elfn32-mips.c (elf_mips16_howto_table_rel): Likewise.
	(elf_mips16_howto_table_rela): Likewise.
	(mips16_reloc_map): Likewise.
	* elfxx-mips.c (mips16_branch_reloc_p): New function.
	(mips16_reloc_p): Handle R_MIPS16_PC16_S1.
	(b_reloc_p): Likewise.
	(mips_elf_calculate_relocation): Likewise.
	(_bfd_mips_elf_check_relocs): Likewise.
	* reloc.c (BFD_RELOC_MIPS16_16_PCREL_S1): New relocation.
	* bfd-in2.h: Regenerate.
	* libbfd.h: Regenerate.

	gas/
	* config/tc-mips.c (mips16_reloc_p): Handle
	BFD_RELOC_MIPS16_16_PCREL_S1.
	(b_reloc_p): Likewise.
	(limited_pcrel_reloc_p): Likewise.
	(md_pcrel_from): Likewise.
	(md_apply_fix): Likewise.
	(tc_gen_reloc): Likewise.
	(md_convert_frag): Likewise.
	(mips_fix_adjustable): Update comment.
	* testsuite/gas/mips/mips16-branch-reloc-2.d: Remove error
	output, add dump patterns.
	* testsuite/gas/mips/mips16-branch-reloc-3.d: Remove error
	output, add dump patterns.
	* testsuite/gas/mips/mips16-branch-addend-2.d: Remove error
	output, add dump patterns.
	* testsuite/gas/mips/mips16-branch-addend-3.d: Remove error
	output, add dump patterns.
	* testsuite/gas/mips/mips16-branch-absolute.d: Remove error
	output, add dump patterns.
	* testsuite/gas/mips/mips16-branch-reloc-2.l: Remove file.
	* testsuite/gas/mips/mips16-branch-reloc-3.l: Remove file.
	* testsuite/gas/mips/mips16-branch-addend-2.l: Remove file.
	* testsuite/gas/mips/mips16-branch-addend-3.l: Remove file.
	* testsuite/gas/mips/mips16-branch-absolute.l: Remove file.
	* testsuite/gas/mips/mips16-branch-addend-2.s: Add padding.
	* testsuite/gas/mips/branch-weak.s: Adjust alignment, avoid
	implicit instruction padding, avoid MIPS16 JR->JRC conversion.
	* testsuite/gas/mips/branch-weak-6.d: New test.
	* testsuite/gas/mips/branch-weak-7.d: New test.
	* testsuite/gas/mips/mips.exp: Run the new tests.

	ld/
	* testsuite/ld-mips-elf/mips16-branch-2.d: New test.
	* testsuite/ld-mips-elf/mips16-branch-3.d: New test.
	* testsuite/ld-mips-elf/mips16-branch-addend-2.d: New test.
	* testsuite/ld-mips-elf/mips16-branch-addend-3.d: New test.
	* testsuite/ld-mips-elf/mips16-branch.s: New test source.
	* testsuite/ld-mips-elf/mips-elf.exp: Run the new tests.