* c-decl.c (mesg_implicit_function_declaration): Init to -1.
	(implicit_decl_warning): New function.
	(implicitly_declare): Use it.
	* c-typeck.c (build_external_ref): Use implicit_decl_warning
	to complain about implicit decls of builtins.

	* c-lang.c (lang_init): Set mesg_implicit_function_declaration
	based on pedantic && flag_isoc99, if not already set.
	* c-tree.h: Declare mesg_implicit_function_declaration.
	Prototype implicit_decl_warning.

	* gcc.dg/c99-impl-decl-1.c: No longer XFAIL.

From-SVN: r35385