ART: Enable bugprone-unused-return-value

Enable bugprone-unused-return-value as an error. This is on top of
the compiler warning for attribute((warn_unused)).

Mark the current occurrences (all unique_ptr.release()) with NOLINT
to signal that we know what we're doing.

Bug: 32619234
Bug: 117926937
Test: WITH_TIDY=1 mmma art
Change-Id: I36659722335eef36acfa5845289104257a393874
diff --git a/runtime/class_loader_context.cc b/runtime/class_loader_context.cc
index 4da0091..5c8d685 100644
--- a/runtime/class_loader_context.cc
+++ b/runtime/class_loader_context.cc
@@ -64,10 +64,10 @@
     // make sure we do not de-allocate them.
     for (ClassLoaderInfo& info : class_loader_chain_) {
       for (std::unique_ptr<OatFile>& oat_file : info.opened_oat_files) {
-        oat_file.release();
+        oat_file.release();  // NOLINT b/117926937
       }
       for (std::unique_ptr<const DexFile>& dex_file : info.opened_dex_files) {
-        dex_file.release();
+        dex_file.release();  // NOLINT b/117926937
       }
     }
   }