re PR c++/64767 (Could GCC warn when a pointer is compared against '\0'?)

re PR c++/64767 (Could GCC warn when a pointer is compared against '\0'?)

	PR c++/64767
	* c.opt (Wpointer-compare): New option.

	* c-parser.c (c_parser_postfix_expression): Mark zero character
	constants by setting original_type in c_expr.
	* c-typeck.c (parser_build_binary_op): Warn when a pointer is compared
	with a zero character constant.
	(char_type_p): New function.

	* typeck.c (cp_build_binary_op): Warn when a pointer is compared with
	a zero character literal.

	* doc/invoke.texi: Document -Wpointer-compare.

	* c-c++-common/Wpointer-compare-1.c: New test.

From-SVN: r244076