Referencing a function's address on PowerPC64 ELFv2

Referencing a function's address on PowerPC64 ELFv2

ELFv2 needs to create plt entries in a non-PIC executable for an
address reference to a function defined in a shared object.  It's
possible that an object file has no features that distinguish it as
ELFv1 or ELFv2, eg. an object only containing data.  Such files need
to be handled like those that are known to be ELFv2.
However, this unnecessarily creates plt entries for the analogous
ELFv1 case, so arrange to set output abi version earlier, and use the
output abi version to further distinguish ambiguous input files.

bfd/
	* elf64-ppc.c (ppc64_elf_check_relocs): Account for possibly
	needed plt entries when taking the address of functions for
	abiversion == 0 (ie. unknown) as well as abiversion == 2.
	Move opd setup and abiversion checks to..
	(ppc64_elf_before_check_relocs): ..here.  Renamed from
	ppc64_elf_process_dot_syms.  Set output abiversion from input and
	input abiversion from output, if either is not set.
	(ppc64_elf_merge_private_bfd_data): Don't merge flags here.
	(elf_backend_check_directives): Update.
ld/testsuite/
	* ld-powerpc/startv1.s, * ld-powerpc/startv2.s, * ld-powerpc/funref.s,
	* ld-powerpc/funv1.s, * ld-powerpc/funv2.s,
	* ld-powerpc/ambiguousv1.d, * ld-powerpc/ambiguousv2.d: New test files.
	* ld-powerpc/powerpc.exp: Run new tests.