ARM & MIPS: Don't embed an address in the general class id fetch.

runtime/vm/assembler_arm.cc

Index: runtime/vm/assembler_arm.cc
diff --git a/runtime/vm/assembler_arm.cc b/runtime/vm/assembler_arm.cc
index 8b5ddccc975c1b7c287a60aefdb3440899cd9aa4..afb5744960a19789ed8a5b8d27763062f13fd6f7 100644
--- a/runtime/vm/assembler_arm.cc
+++ b/runtime/vm/assembler_arm.cc
@@ -2009,12 +2009,9 @@ void Assembler::CompareClassId(Register object,
 
 
 void Assembler::LoadClassIdMayBeSmi(Register result, Register object) {
-  static const intptr_t kSmiCidSource = kSmiCid << RawObject::kClassIdTagPos;
-
-  LoadImmediate(TMP, reinterpret_cast<int32_t>(&kSmiCidSource) + 1);
   tst(object, Operand(kSmiTagMask));
-  mov(TMP, Operand(object), NE);
-  LoadClassId(result, TMP);
+  LoadClassId(result, object, NE);
+  LoadImmediate(result, kSmiCid, EQ);
 }