Objective-C, Darwin : Update message call codegen.

Objective-C, Darwin : Update message call codegen.

Platform compilers based on LLVM do not use the objc_sendMsg_fixit
and friends for newer editions of the OS (runtimes for Arm64 do not even
have those entries).

We need to arrange to allow for this codegen on modern Darwin.

The _fixit versions are needed for some OS versions (at least, up to
10.6) since the super2 call is not implemented there.  It does not
seem worth making the codegen more fine-grained at present.

Other parts of the codegen need to be made conditional on either the
runtime version or the linker capabilities.

gcc/objc/ChangeLog:

	* objc-next-runtime-abi-02.c (TAG_MSGSENDSUPER): Revised
	spelling.
	(TAG_MSGSENDID): Likewise.
	(TAG_MSGSENDSUPER_STRET): Likewise.
	(TAG_MSGSENDID_STRET): Likewise.
	(FIXUP_NEEDED): Likewise.
	(TAG_FIXUP): New.
	(next_runtime_02_initialize): Adjust message calls to use
	fixup variants only when required.
	(next_runtime_abi_02_get_arg_type_list_base): Correct
	indent.
	(build_v2_build_objc_method_call): New.
	(build_v2_objc_method_fixup_call): Split out from ...
	(next_runtime_abi_02_build_objc_method_call): ... here.
	Arrange to adjust the call on the basis of the target
	runtime.