Objective-C, Darwin : Update metadata section uses.

Objective-C, Darwin : Update metadata section uses.

Newer versions of ld64 are more picky about adherence to placement
rules for objective c metadata.  This adds protocol refs and uses
the ivar refs for all targets.

gcc/ChangeLog:

	* config/darwin-sections.def (objc2_data_section): New.
	(objc2_ivar_section): New.
	* config/darwin.c (darwin_objc2_section): Act on Protocol and
	ivar refs.

gcc/objc/ChangeLog:

	* objc-next-runtime-abi-02.c
	(next_runtime_abi_02_init_metadata_attributes): Make protocol
	refs a distinct section.