Enabled linkonce support for Darwin.

Enabled linkonce support for Darwin.

	* target.h (struct gcc_target): New target hook, unwind_label.
	* target-def.h (TARGET_ASM_EMIT_UNWIND_LABEL): New hook.
	* output.h (default_emit_unwind_label): New function.
	* default.h (TARGET_EXPLICIT_INSTANTIATIONS_ONE_ONLY): New macro.
	(TARGET_USES_WEAK_UNWIND_INFO): New target macro.
	(TARGET_SUPPORTS_HIDDEN): New target macro.
	* dwarf2out.c (struct dw_fde_struct): Add field for function decl
	that corresponds to this FDE.
	(FRAME_BEGIN_LABEL): Allow target to override default label.
	(output_call_frame_info): If FDEs are linknonce, then use extra
	indirection for FDE encoding, output a label for each FDE, and
	output an empty label for each function without an FDE.
	(dwarf2out_begin_prologue): Set up decl field when creating an FDE.
	* varasm.c (globalize_decl): Call ASM_MAKE_LABEL_LINKONCE for
	decls with DECL_ONE_ONLY set, if that macro is defined.
	(make_decl_one_only): Don't use DECL_COMMON if we're compiling
	for a SUPPORTS_ONE_ONLY target.
	* config/darwin-protos.h (darwin_unique_section): Declare.
	(darwin_asm_named_section): Likewise.
	(darwin_section_type_flags): Likewise.
	(darwin_non_lazy_pcrel): Likewise.
	(darwin_emit_unwind_label): Likewise.
	(darwin_make_decl_one_only): Likewise.
	* config/darwin.c (machopic_finish): Get rid of tweak that
	eliminate stubs for symbols that are defined.
	(darwin_encode_section_info): Don't treat weak functions as defined.
	(darwin_make_decl_one_only): Define.
	(darwin_asm_named_section): Likewise.
	(darwin_section_type_flags): Likewise.
	(darwin_unique_section): Likewise.
	(darwin_emit_unwind_label): Likewise.
	(darwin_non_lazy_pcrel): Likewise.
	(darwin_asm_output_dwarf_delta): Difference between two labels is
	local only if both labels are local.
	* config/darwin.h (MAKE_DECL_ONE_ONLY): Define.
	(ASM_MAKE_LABEL_LINKONCE): Likewise.
	(TARGET_SUPPORTS_HIDDEN): Likewise.
	(TARGET_USES_WEAK_UNWIND_INFO): Likewise.
	(TARGET_EXPLICIT_INSTANTIATIONS_ONE_ONLY): Likewise.
	(FRAME_BEGIN_LABEL): Likewise.
	(ASM_DECLARE_OBJECT_NAME): Make references to weak symbols indirect.
	(ASM_DECLARE_FUNCTION_NAME): Likewise.
	(darwin_eh_frame_section): Give __eh_frame section the coalesced flag.
	(TARGET_ASM_UNIQUE_SECTION): Define.
	(EH_FRAME_SECTION_NAME): Define.
	(EH_FRAME_SECTION_ATTR): Likewise.
	(ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX): Likewise.
	(TARGET_ASM_NAMED_SECTION): Likewise.
	(TARGET_SECTION_TYPE_FLAGS): Likewise.
	* doc/tm.texi: Document TARGET_USES_WEAK_UNWIND_INFO,
	TARGET_EXPLICIT_INSTANTIATIONS_ONE_ONLY, TARGET_SUPPORTS_HIDDEN,
	TARGET_ASM_EMIT_UNWIND_LABEL.

	* cp/decl2.c (maybe_make_one_only): Look at
	TARGET_EXPLICIT_INSTANTIATION_ONE_ONLY when deciding whether
	to make an explicit instantiation weak.
	* cp/method.c (use_thunk): Make sure we call comdat_linkage
	when appropriate.
	* cp/pt.c (do_type_instantiation): On systems where weak symbols
	don't go in a static archive's TOC, explicit instantiation of a
	class must imply *explicit* instantiation of its memeber.

From-SVN: r79394