For ARMv6, works around missing instructions.

runtime/vm/assembler_arm.h

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_ASSEMBLER_ARM_H_
 #define VM_ASSEMBLER_ARM_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_arm.h directly; use assembler.h instead.
 #endif
@@ skipping 575 matching lines @@
   void CompareImmediate(Register rn, int32_t value, Condition cond = AL);
 
 
   // Signed integer division of left by right. Checks to see if integer
   // division is supported. If not, uses the FPU for division with
   // temporary registers tmpl and tmpr. tmpl and tmpr must be different
   // registers.
   void IntegerDivide(Register result, Register left, Register right,
                      DRegister tmpl, DRegister tmpr);
 
+  // If we aren't on ARMv7, there is no smull.
+  void CheckMultSignedOverflow(Register left,
+                               Register right,
+                               Register tmp,
+                               DRegister dtmp0, DRegister dtmp1,
+                               Label* overflow);
+
   // Load and Store. May clobber IP.
   void LoadPatchableImmediate(Register rd, int32_t value, Condition cond = AL);
   void LoadDecodableImmediate(Register rd, int32_t value, Condition cond = AL);
   void LoadImmediate(Register rd, int32_t value, Condition cond = AL);
   void LoadSImmediate(SRegister sd, float value, Condition cond = AL);
   void LoadDImmediate(DRegister dd, double value,
                       Register scratch, Condition cond = AL);
 
   void MarkExceptionHandler(Label* label);
 
@@ skipping 292 matching lines @@
                                   Register value,
                                   Label* no_update);
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Assembler);
 };
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_ARM_H_