c-common.c (c_common_truthvalue_conversion): When warning about using an assignment as a truth value, set TREE_NO_WARNING.

./:	* c-common.c (c_common_truthvalue_conversion): When warning about
	using an assignment as a truth value, set TREE_NO_WARNING.
cp/:
	* semantics.c (maybe_convert_cond): Optionally warn when using an
	assignment as a condition.
	* typeck.c (convert_for_assignment): Optionally warn about
	assigning the result of an assignment to a bool.
testsuite/:
	* g++.dg/warn/Wparentheses-22.C: New test.
	* g++.dg/warn/Wparentheses-23.C: New test.

From-SVN: r120348