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.

gcc/testsuite/g++.dg/uninit-pr74762.C

+/* PR c++/74762 - missing uninitialized warning (C++, parenthesized expr)
+   { dg-do compile }
+   { dg-options "-Wall" } */
+
+struct tree2;
+struct tree_vector2
+{
+  tree2 *elts[1];
+};
+
+struct tree2
+{
+  struct
+  {
+    tree_vector2 vector;
+  } u;
+};
+
+tree2 *
+const_with_all_bytes_same (tree2 *val)
+{
+  int i;
+  return ((val->u.vector.elts[i]));   // { dg-warning "\\\[-Wuninitialized" }
+}

gcc/testsuite/g++.dg/warn/uninit-pr74765.C

+/* PR c++/74765 - missing uninitialized warning (parenthesis,
+   TREE_NO_WARNING abuse)
+   { dg-do compile }
+   { dg-options "-Wall" } */
+
+int warn_equal_parens (int x, int y)
+{
+  int i;
+
+  if ((i == 0))     // { dg-warning "\\\[-Wuninitialized" }
+    return x;
+
+  return y;
+}
+
+int warn_equal (int x, int y)
+{
+  int i;
+
+  if (i == 0)       // { dg-warning "\\\[-Wuninitialized" }
+    return x;
+
+  return y;
+}