Fix a harmless assert and a genuine bug in the GC-safety of stub

src/arm/code-stubs-arm.h

Index: src/arm/code-stubs-arm.h
===================================================================
--- src/arm/code-stubs-arm.h	(revision 9318)
+++ src/arm/code-stubs-arm.h	(working copy)
@@ -323,6 +323,9 @@
         the_heap_number_(the_heap_number),
         scratch_(scratch) { }
 
+  bool CompilingCallsToThisStubIsGCSafe();
+  static void GenerateStubsAheadOfTime();
+
  private:
   Register the_int_;
   Register the_heap_number_;