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/utils/arm/assembler_arm_vixl.cc b/compiler/utils/arm/assembler_arm_vixl.cc
index 8045bd2..e3b9fb6 100644
--- a/compiler/utils/arm/assembler_arm_vixl.cc
+++ b/compiler/utils/arm/assembler_arm_vixl.cc
@@ -62,6 +62,12 @@
   ___ Rsb(reg, reg, 0);
 }
 
+void ArmVIXLAssembler::MaybePoisonHeapReference(vixl32::Register reg) {
+  if (kPoisonHeapReferences) {
+    PoisonHeapReference(reg);
+  }
+}
+
 void ArmVIXLAssembler::MaybeUnpoisonHeapReference(vixl32::Register reg) {
   if (kPoisonHeapReferences) {
     UnpoisonHeapReference(reg);