re PR c/65120 (Wlogical-not-parentheses should not warn about double exclamation !!)

re PR c/65120 (Wlogical-not-parentheses should not warn about double exclamation !!)

	PR c/65120
	* c-common.c (warn_logical_not_parentheses): Don't warn for
	!x == 0 or !x != 0.

	* c-typeck.c (parser_build_binary_op): Check for tcc_comparison
	before preparing arguments to warn_logical_not_parentheses.

	* parser.c (cp_parser_binary_expression): Check for tcc_comparison
	before preparing arguments to warn_logical_not_parentheses.
	Use maybe_constant_value on rhs.

	* c-c++-common/pr49706.c (fn2): Don't expect warning if enumerator
	on rhs is 0.
	(fn4): New test.
	* c-c++-common/pr65120.c: New test.

From-SVN: r221299