[GOLD] PowerPC64 tocsave

[GOLD] PowerPC64 tocsave

This adds support to gold for the tocsave relocs already supported by
ld.bfd.  R_PPC64_TOCSAVE relocs are part of a scheme to move r2 saves
to the prologue of a function rather than in each plt call stub.  We
don't want a compiler to always emit the r2 save, as this would be
wasted if the calls turned out to be local.  See the tocsave*.s in
ld/testsuite/ld-powerpc/.

	* powerpc.cc (Target_powerpc::tocsave_loc_): New var.
	(Target_powerpc::mark_pltcall, add_tocsave, tocsave_loc): New functions.
	(Target_powerpc::Branch_info::tocsave_): New var.
	(Target_powerpc::Branch_info::mark_pltcall): New function.
	(Target_powerpc::Branch_info::make_stub): Pass tocsave_ to
	add_plt_call_entry.
	(Stub_table::Plt_stub_ent): Make public.  Add r2save_.
	(Stub_table::add_plt_call_entry): Add bool tocsave_ param.  Set
	r2save_.
	(Stub_table::find_plt_call_entry): Return Plt_stub_ent*.  Adjust
	use throughout.
	(Stub_table::do_write): Conditionally output r2 save in plt stubs.
	(Target_powerpc::Scan::local): Handle R_PPC64_TOCSAVE.
	(Target_powerpc::Scan::global): Likewise.
	(Target_powerpc::Relocate::relocate): Skip r2 save in plt call stub
	with tocsave reloc.  Replace header tocsave nop with r2 save.
	* symtab.h (struct Symbol_location_hash): Make public.