No gcc, please don't optimize away the stack overflow check.

runtime/vm/dart_entry.cc

Index: runtime/vm/dart_entry.cc
diff --git a/runtime/vm/dart_entry.cc b/runtime/vm/dart_entry.cc
index 4ae6851f5b194244eee3d29b7087084a557a50fc..de926bfe9271461af65b65be583845ba953517d2 100644
--- a/runtime/vm/dart_entry.cc
+++ b/runtime/vm/dart_entry.cc
@@ -168,9 +168,9 @@ RawObject* DartEntry::InvokeClosure(const Array& arguments,
       function ^= cls.LookupDynamicFunction(getter_name);
       if (!function.IsNull()) {
         Isolate* isolate = Isolate::Current();
-        uword c_stack_pos = Isolate::GetCurrentStackPointer();
-        uword c_stack_limit = OSThread::Current()->stack_base() -
-                              OSThread::GetSpecifiedStackSize();
+        volatile uword c_stack_pos = Isolate::GetCurrentStackPointer();
+        volatile uword c_stack_limit = OSThread::Current()->stack_base() -
+                                       OSThread::GetSpecifiedStackSize();
 #if !defined(USING_SIMULATOR)
         ASSERT(c_stack_limit == isolate->saved_stack_limit());
 #endif