ARM: VIXL32: Implement the functionality needed by intrinsics.

This patch passes:
* 004-UnsafeTest

Test: ART_USE_VIXL_ARM_BACKEND=true m test-art-host
Test: ART_USE_VIXL_ARM_BACKEND=true m test-art-target
Change-Id: I7a3cd410411ef3a520d419734a835090097b2aee
diff --git a/compiler/optimizing/common_arm.h b/compiler/optimizing/common_arm.h
index 8c08a9c..13824ad 100644
--- a/compiler/optimizing/common_arm.h
+++ b/compiler/optimizing/common_arm.h
@@ -135,6 +135,16 @@
   return InputRegisterAt(instr, 0);
 }
 
+inline int32_t Int32ConstantFrom(Location location) {
+  HConstant* instr = location.GetConstant();
+  if (instr->IsIntConstant()) {
+    return instr->AsIntConstant()->GetValue();
+  } else {
+    DCHECK(instr->IsNullConstant()) << instr->DebugName();
+    return 0;
+  }
+}
+
 inline int64_t Int64ConstantFrom(Location location) {
   HConstant* instr = location.GetConstant();
   if (instr->IsIntConstant()) {