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

Bug: http://b/111067277
Test: builds
Change-Id: I8b69ea3815e14bb6eb27f40c0dd01a85b340a355
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index 48b50ea..bbf167d 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -3046,7 +3046,7 @@
 
   if (!DataType::IsIntegralType(type)) {
     LOG(FATAL) << "Unexpected type " << type << " for DivZeroCheck.";
-    return;
+    UNREACHABLE();
   }
 
   if (value.IsConstant()) {