[gn] Enable stricter build flags

src/runtime/runtime-liveedit.cc

Index: src/runtime/runtime-liveedit.cc
diff --git a/src/runtime/runtime-liveedit.cc b/src/runtime/runtime-liveedit.cc
index 56493252c8fd57cffb74977c154bb6c9e26efc30..fa49df88dada9240d42e58cc01986a8808de0b53 100644
--- a/src/runtime/runtime-liveedit.cc
+++ b/src/runtime/runtime-liveedit.cc
@@ -32,7 +32,7 @@ RUNTIME_FUNCTION(Runtime_LiveEditFindSharedFunctionInfosForScript) {
   {
     HeapIterator iterator(heap);
     HeapObject* heap_obj;
-    while ((heap_obj = iterator.next())) {
+    while ((heap_obj = iterator.next()) != nullptr) {
       if (!heap_obj->IsSharedFunctionInfo()) continue;
       SharedFunctionInfo* shared = SharedFunctionInfo::cast(heap_obj);
       if (shared->script() != *script) continue;