PR opt/4330
        * langhooks.h (lang_hooks.decls.warn_unused_global): New.
        * toplev.c (check_global_declarations): Use it.
        * langhooks-def.h (lhd_warn_unused_global_decl): Declare.
        (LANG_HOOKS_WARN_UNUSED_GLOBAL_DECL): New.
        (LANG_HOOKS_DECLS): Add it.
        * langhooks.c (lhd_warn_unused_global_decl): New.
        * c-decl.c (LANG_HOOKS_WARN_UNUSED_GLOBAL_DECL): New.
        * c-objc-common.c (c_warn_unused_global_decl): New.
        * c-tree.h (c_warn_unused_global_decl): Declare.
        * objc/objc-lang.c (LANG_HOOKS_WARN_UNUSED_GLOBAL_DECL): New.

        * cp-lang.c (cxx_warn_unused_global_decl): New.
        (LANG_HOOKS_WARN_UNUSED_GLOBAL_DECL): New.

	* g++.dg/warn/Wunused-2.C: New.
	* gcc.dg/unused-4.c: New.

From-SVN: r51818