PR c/15698
	* c-tree.h (C_DECL_BUILTIN_PROTOTYPE): New.
	* c-decl.c (current_function_prototype_built_in,
	current_function_prototype_arg_types): New.
	(merge_decls): Keep source location of prototype followed by
	nonprototype declaration.  Update C_DECL_BUILTIN_PROTOTYPE.
	(builtin_function): Set C_DECL_BUILTIN_PROTOTYPE.
	(start_function): Always set current_function_prototype_locus,
	current_function_prototype_built_in and
	current_function_prototype_arg_types.  Check for external
	prototype whether or not visible for external function and set
	current_function_prototype_arg_types accordingly.
	(store_parm_decls_oldstyle): Use
	current_function_prototype_arg_types for checking old-style
	definition against prototype.  Give warnings only if
	current_function_prototype_built_in).

testsuite:
	* gcc.dg/builtins-30.c: Update expected messages.
	* gcc.dg/pr15698-1.c, gcc.dg/pr15698-2.c, gcc.dg/pr15698-3.c,
	gcc.dg/pr15698-4.c, gcc.dg/pr15698-5.c, gcc.dg/pr15698-6.c,
	gcc.dg/pr15698-7.c, pr15698-8.c: New tests.

From-SVN: r99118