The libc++ upgrade lets us use contains() in tests now.

Change-Id: I2999aad2cc186c34037dcea4b8a587d868aabda3
diff --git a/tests/link_test.cpp b/tests/link_test.cpp
index 127a3d9..ae3a1cd 100644
--- a/tests/link_test.cpp
+++ b/tests/link_test.cpp
@@ -195,7 +195,7 @@
     }
     void AddModule(dl_phdr_info* info, size_t s) {
       ASSERT_EQ(sizeof(dl_phdr_info), s);
-      ASSERT_TRUE(dl_iter_mods.find(info->dlpi_addr) == dl_iter_mods.end());
+      ASSERT_FALSE(dl_iter_mods.contains(info->dlpi_addr));
       ASSERT_TRUE(info->dlpi_name != nullptr);
       dl_iter_mods[info->dlpi_addr] = {
         .name = info->dlpi_name,