[libcxx-test] make constants unsigned to match values

Bug: 138738352
Change-Id: I5d0c1803afed6545bba75cbc7fa9ba9297a4dc8d
diff --git a/libcxx-test/libcxx_test.cpp b/libcxx-test/libcxx_test.cpp
index eb18b22..5447973 100644
--- a/libcxx-test/libcxx_test.cpp
+++ b/libcxx-test/libcxx_test.cpp
@@ -279,13 +279,13 @@
     std::vector<Counter> b;
 
     EXPECT_EQ(3, global_count);
-    EXPECT_EQ(3, a.size());
-    EXPECT_EQ(0, b.size());
+    EXPECT_EQ(3U, a.size());
+    EXPECT_EQ(0U, b.size());
 
     b = std::move(a);
 
     // Note: can't say much about the state of "a".
-    EXPECT_EQ(3, b.size());
+    EXPECT_EQ(3U, b.size());
 
     a = {};
     b = {};