or1k: Avoid R_OR1K_GOT16 signed overflow by using special howto

or1k: Avoid R_OR1K_GOT16 signed overflow by using special howto

Previously when fixing PR 21464 we masked out upper bits of the
relocation value in order to avoid overflow complaints when acceptable.
It turns out this does not work when the relocation value ends up being
signed.

To fix this this patch introduces a special howto with
complain_on_overflow set to complain_overflow_dont.  This is used in
place of the normal R_OR1K_GOT16 howto when we detect R_OR1K_GOT_AHI16
relocations.

bfd/ChangeLog:

	PR 28735
	* elf32-or1k.c (or1k_elf_got16_no_overflow_howto): Define.
	(or1k_elf_relocate_section): Use new howto instead of trying to
	mask out relocation bits.