c++: Add test for Core issue 1376 [PR52202]

As Jens says in the PR, we handle this correctly.

gcc/testsuite/ChangeLog:

	PR c++/52202
	* g++.dg/cpp0x/rv-life.C: New test.

gcc/testsuite/g++.dg/cpp0x/rv-life.C

+// Core 1376
+// PR c++/52202
+// { dg-do run { target c++11 } }
+
+extern "C" void abort();
+bool x;
+struct T { ~T() { if (!x) abort (); } };
+int main()
+{
+  T&& r = static_cast<T&&>(T());
+  x = true;
+}