MIPS: Correct HI/LO rel reloc howto special_function entries

MIPS: Correct HI/LO rel reloc howto special_function entries

This corrects the DTPREL_HI16/LO16 and TPREL_HI16/LO16 howtos to use
_bfd_mips_elf_{hi,lo}16_reloc special functions, in order to support
addends outside the range [0,32767] on these relocations.

R_MIPS_GOT_HI16, R_MIPS_GOT_LO16, R_MIPS_CALL_HI16 and R_MIPS_CALL_LO16
are left alone as it seems that we (quite reasonably) only support
zero addends for those relocs.

	PR 19977
bfd/
	* elf32-mips.c (elf_mips_howto_table_rel): Set special_function
	to _bfd_mips_elf_hi16_reloc for R_MIPS_TLS_DTPREL_HI16 and
	R_MIPS_TLS_TPREL_HI16.  Set special_function to
	_bfd_mips_elf_lo16_reloc for R_MIPS_TLS_DTPREL_LO16 and
	R_MIPS_TLS_TPREL_LO16
	(elf_mips16_howto_table_rel): Likewise for
	R_MIPS16_TLS_DTPREL_HI16, R_MIPS16_TLS_DTPREL_LO16,
	R_MIPS16_TLS_TPREL_HI16 and R_MIPS16_TLS_TPREL_LO16.
	(elf_micromips_howto_table_rel): Likewise for
	R_MICROMIPS_TLS_DTPREL_HI16, R_MICROMIPS_TLS_DTPREL_LO16,
	R_MICROMIPS_TLS_TPREL_HI16 and R_MICROMIPS_TLS_TPREL_LO16.
	* elf64-mips.c (mips_elf64_howto_table_rel): Similarly.
	(mips16_elf64_howto_table_rel): Similarly.
	(micromips_elf64_howto_table_rel): Similarly.
	* elfn32-mips.c: As for elf64-mips.c.
gas/
	* testsuite/gas/mips/pr19977.d,
	* testsuite/gas/mips/pr19977.s: New test.
	* testsuite/gas/mips/mips.exp: Run it.