PR c/7776
	* common.opt (Wstring-literal-comparison): New command line option.
	* c-opts.c (c_common_handle_option): Set it with -Wall.
	* c-typeck.c (parser_build_binary_op): Issue warning if either
	operand of a comparison operator is a string literal, except for
	testing equality or inequality against NULL.

	* doc/invoke.texi: Document new -Wstring-literal-comparison option.

	* gcc.dg/Wstring-literal-comparison-1.c: New test case.
	* gcc.dg/Wstring-literal-comparison-2.c: Likewise.
	* gcc.dg/Wstring-literal-comparison-3.c: Likewise.
	* gcc.dg/Wstring-literal-comparison-4.c: Likewise.

From-SVN: r108018