PowerPC PLT stub tidy

This is in preparation for the next patch adding Spectre variant 2
mitigation for PowerPC and PowerPC64.  Besides tidying code involved
in stub output (to reduce the number of places where bctr is output),
the patch adds some user visible features:

1) PowerPC64 ELFv2 global entry stubs now are aligned under the
   control of --plt-align, with a default alignment of 32 bytes.
2) PowerPC64 __glink_PLTresolve is no longer padded out with nops.
3) PowerPC32 PLT stubs are aligned under the control of --plt-align,
   with the default alignment being 16 bytes as before.
4) The PowerPC32 branch/nop table emitted before __glink_PLTresolve
   is now smaller in many cases.  It was sized incorrectly when the
   __tls_get_addr_opt stub was used, and unnecessarily included space
   for local ifuncs.

bfd/
	* elf32-ppc.c (GLINK_ENTRY_SIZE): Add parameters, handle
	__tls_get_addr_opt, and alignment sizing.
	(TLS_GET_ADDR_GLINK_SIZE): Delete.
	(is_nonpic_glink_stub): Don't use GLINK_ENTRY_SIZE.
	(ppc_elf_get_synthetic_symtab): Recognize stubs spaced at 4, 6,
	or 8 insns.
	(ppc_elf_link_hash_table_create): Init new ppc_elf_params field.
	(allocate_dynrelocs): Use new GLINK_ENTRY_SIZE.
	(ppc_elf_size_dynamic_sections): Likewise.  Size branch table
	by PLT reloc count.
	(write_glink_stub): Handle __tls_get_addr_opt stub.
	Pad out to size given by GLINK_ENTRY_SIZE.
	(ppc_elf_relocate_section): Adjust write_glink_stub call.
	(ppc_elf_finish_dynamic_symbol): Likewise.
	(ppc_elf_finish_dynamic_sections): Write PLTresolve without using
	insn array since so many need rewriting.
	* elf32-ppc.h (struct ppc_elf_params): Add plt_stub_align.
	* elf64-ppc.c (GLINK_PLTRESOLVE_SIZE): Rename from
	GLINK_CALL_STUB_SIZE.  Add htab param and evaluate to size without
	nops.  Adjust all uses.
	(ppc64_elf_get_synthetic_symtab): Don't use GLINK_CALL_STUB_SIZE
	in glink_vma calculation.
	(struct ppc_link_hash_table): Add global_entry section pointer.
	(create_linkage_sections): Create separate section for global
	entry stubs.
	(PPC_LO, PPC_HI, PPC_HA): Move earlier.
	(size_global_entry_stubs): Handle sizing for aligned stubs.
	(ppc64_elf_size_dynamic_sections): Handle global_entry alloc,
	and don't stash end of glink branch table in rawsize.
	(ppc_build_one_stub): Rewrite stub size calculations.
	(build_global_entry_stubs): Use new section.
	(ppc64_elf_build_stubs): Don't pad __glink_PLTresolve with nops.
	Build lazy link stubs out to end of section.  Build global entry
	stubs in new section.
gold/
	* options.h (plt_align): Support for PowerPC32 too.
	* powerpc.cc (Stub_table::stub_align): Heed --plt-align for 32-bit.
	(Stub_table::plt_call_size, branch_stub_size): Tidy.
	(Stub_table::plt_call_align): Implement using stub_align.
	(Output_data_glink::global_entry_align): New function.
	(Output_data_glink::global_entry_off): New function.
	(Output_data_glink::global_entry_address): Use global_entry_off.
	(Output_data_glink::pltresolve_size): New function, replacing
	pltresolve_size_ constant.  Update all uses.
	(Output_data_glink::add_global_entry): Align offset.
	(Output_data_glink::set_final_data_size): Use global_entry_align.
	(Stub_table::do_write): Don't pad __glink_PLTrelsolve with nops.
	Tidy stub output.  Use global_entry_off.
ld/
	* emultempl/ppc32elf.em (params): Init new field.
	(enum ppc32_opt): New enum to define OPTION_* values.  Add
	OPTION_PLT_ALIGN and OPTION_NO_PLT_ALIGN.
	(PARSE_AND_LIST_LONGOPTS): Handle new options.
	(PARSE_AND_LIST_ARGS_CASES): Likewise.
	(PARSE_AND_LIST_OPTIONS): Likewise.  Break up help output.
	* emultempl/ppc64elf.em (ppc_add_stub_section): Init alignment
	correctly for negative --plt-stub-align.
	* testsuite/ld-powerpc/elfv2exe.d,
	* testsuite/ld-powerpc/elfv2so.d,
	* testsuite/ld-powerpc/relbrlt.d,
	* testsuite/ld-powerpc/relbrlt.s,
	* testsuite/ld-powerpc/tlsexe.d,
	* testsuite/ld-powerpc/tlsexe.r,
	* testsuite/ld-powerpc/tlsexe32.d,
	* testsuite/ld-powerpc/tlsexe32.g,
	* testsuite/ld-powerpc/tlsexe32.r,
	* testsuite/ld-powerpc/tlsexetoc.d,
	* testsuite/ld-powerpc/tlsexetoc.r,
	* testsuite/ld-powerpc/tlsopt5_32.d,
	* testsuite/ld-powerpc/tlsso.d,
	* testsuite/ld-powerpc/tlstocso.d: Update for changed stub order.

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