[libcxx] Fix pop_back() tests to make sure they don't always just pass

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@349071 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/libcxx/containers/sequences/deque/pop_back_empty.pass.cpp b/test/libcxx/containers/sequences/deque/pop_back_empty.pass.cpp
index 1435f95..e4f5d0b 100644
--- a/test/libcxx/containers/sequences/deque/pop_back_empty.pass.cpp
+++ b/test/libcxx/containers/sequences/deque/pop_back_empty.pass.cpp
@@ -22,4 +22,5 @@
     q.push_back(0);
     q.pop_back();
     q.pop_back();
+    std::exit(1);
 }
diff --git a/test/libcxx/containers/sequences/vector/pop_back_empty.pass.cpp b/test/libcxx/containers/sequences/vector/pop_back_empty.pass.cpp
index 4714912..388dfa4 100644
--- a/test/libcxx/containers/sequences/vector/pop_back_empty.pass.cpp
+++ b/test/libcxx/containers/sequences/vector/pop_back_empty.pass.cpp
@@ -22,4 +22,5 @@
     v.push_back(0);
     v.pop_back();
     v.pop_back();
+    std::exit(1);
 }