C++17 compatibility: make WITH_TIDY=1 happy again.

Bug: http://b/111067277
Test: builds
Change-Id: I8b69ea3815e14bb6eb27f40c0dd01a85b340a355
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 9cbbd41..ab79b9e 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -1241,7 +1241,6 @@
     }
     case JdwpProvider::kUnset: {
       LOG(FATAL) << "Illegal jdwp provider " << jdwp_provider_ << " was not filtered out!";
-      break;
     }
   }
   callbacks_->AddThreadLifecycleCallback(Dbg::GetThreadLifecycleCallback());
@@ -1856,7 +1855,7 @@
     return 0;  // backward compatibility
   default:
     LOG(FATAL) << "Unknown statistic " << kind;
-    return -1;  // unreachable
+    UNREACHABLE();
   }
 }