Objective-C, NeXT: Adjust symbol marking to match host tools.

Objective-C, NeXT: Adjust symbol marking to match host tools.

Current host tools mark some additional symbols as 'no dead strip' and also
expose one additional group to the linker.  This does not affect older Darwin
versions or x86_64, but omitting these changes results in link errors for
aarch64.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
gcc/ChangeLog:

	* config/darwin.cc (darwin_label_is_anonymous_local_objc_name): Make
	protocol class methods linker-visible.

gcc/objc/ChangeLog:

	* objc-next-runtime-abi-02.cc (next_runtime_abi_02_protocol_decl): Do
	not dead-strip the runtime meta-data symbols.
	(build_v2_classrefs_table): Likewise.
	(build_v2_protocol_list_address_table): Likewise.