Regression tests for TREE_NO_WARNING enhancement to warning groups [PR74765, PR74762].

PR middle-end/74765 - missing uninitialized warning (parenthesis, TREE_NO_WARNING abuse)
PR middle-end/74762 - [9/10/11/12 Regression] missing uninitialized warning (C++, parenthesized expr, TREE_NO_WARNING)

gcc/testsuite/ChangeLog:

	* g++.dg/uninit-pr74762.C: New test.
	* g++.dg/warn/uninit-pr74765.C: Same.