Fix simarm build for newer gcc's

runtime/vm/constants_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 RUNTIME_VM_CONSTANTS_ARM_H_
 #define RUNTIME_VM_CONSTANTS_ARM_H_
 
 #include "platform/globals.h"
 #include "platform/assert.h"
 
@@ skipping 242 matching lines @@
 #if defined(VFPv3_D32)
   ASSERT(d < D16);
 #endif
   return static_cast<SRegister>((d * 2) + 1);
 }
 
 
 // Register aliases for floating point scratch registers.
 const QRegister QTMP = Q7;                     // Overlaps with DTMP, STMP.
 const DRegister DTMP = EvenDRegisterOf(QTMP);  // Overlaps with STMP.
-const SRegister STMP = EvenSRegisterOf(DTMP);
+const SRegister STMP DART_USED = EvenSRegisterOf(DTMP);
 
 // Architecture independent aliases.
 typedef QRegister FpuRegister;
 
 const FpuRegister FpuTMP = QTMP;
 const int kNumberOfFpuRegisters = kNumberOfQRegisters;
 const FpuRegister kNoFpuRegister = kNoQRegister;
 
 // Register aliases.
 const Register TMP = IP;            // Used as scratch register by assembler.
@@ skipping 483 matching lines @@
   static Instr* At(uword pc) { return reinterpret_cast<Instr*>(pc); }
 
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Instr);
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_CONSTANTS_ARM_H_