Pack interpSave struct to fix x86 & Arm diffs

On x86, the double in JValue forces 8-byte alignment, which causes
a problem for our asm-constants.  Pack it.

Change-Id: Ia53c3928a47a127fdfbb12a958111c475f83fbde
diff --git a/vm/interp/InterpState.h b/vm/interp/InterpState.h
index 9997953..9b21bd1 100644
--- a/vm/interp/InterpState.h
+++ b/vm/interp/InterpState.h
@@ -107,7 +107,7 @@
     int             unused;        // Keep struct size constant
 #endif
     struct InterpSaveState* prev;  // To follow nested activations
-};
+} __attribute__ ((__packed__));
 
 #ifdef WITH_JIT
 /*