ucrtbase: Add __std_exception_destroy/copy

[Piotr Caban]

Hi Daniel,

please add following tests (and fix implementation):
+    src.what = NULL;
+    src.dofree = 0;
+    p___std_exception_copy(&src, &dst);
+    ok(!dst.what, "dst.what != NULL\n");
+    ok(!dst.dofree, "dst.dofree != FALSE\n");
+
+    src.what = NULL;
+    src.dofree = 1;
+    p___std_exception_copy(&src, &dst);
+    ok(!dst.what, "dst.what != NULL\n");
+    ok(!dst.dofree, "dst.dofree != FALSE\n");

Thanks,
Piotr