PR22300, Abort in elf32_hppa_relocate_section building polyml

PR22300, Abort in elf32_hppa_relocate_section building polyml

polyml produces object files with the wrong OS/ABI for hppa-linux.
This, along with the fact that elf32-hppa.c is using the strictest
backend relocs_compatible, results in wrong merging of ELF symbols.

So, remove the relocs_compatible check in _bfd_elf_merge_symbol.
_bfd_elf_merge_symbol is only called nowadays from within blocks
protected by is_elf_hash_table, so "we are doing an ELF link" as the
removed comment says, is true.

Also relax relocs_compatible for hppa and powerpc.  relocs_compatible
is used for more than just merging symbols, as the name suggests.
This allows objects that are in fact reasonably compatible to be
linked.

	PR 22300
	* elflink.c (_bfd_elf_merge_symbol): Remove relocs_compatible check.
	* elf32-hppa.c (elf_backend_relocs_compatible): Define.
	* elf32-ppc.c (elf_backend_relocs_compatible): Define.
	* elf64-ppc.c (elf_backend_relocs_compatible): Define.