Objective-C, Darwin : Make protocols private extern and weak.
Newer linkers want protocols to be private-extern and weak.
This is conditional on the runtime version.
gcc/objc/ChangeLog:
* objc-next-runtime-abi-02.c
(create_global_decl): Update to allow the caller to
specify declaration or definition.
(create_hidden_decl): Likewise.
(next_runtime_abi_02_protocol_decl): Make the symbol
weak and hidden for later OS runtime versions.
(build_v2_protocol_list_address_table): Likewise.