Resolve some disagreements between SIMARM and XARM on offsets used in compiled code.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index cef2223f7a70706d4c2ee0ce8684a6ef12f7864f..cbea4f3a8d06b5cb0fcb7fc6f922c3e8136e2617 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -1606,11 +1606,12 @@ class RawSmi : public RawInteger {
 class RawMint : public RawInteger {
   RAW_HEAP_OBJECT_IMPLEMENTATION(Mint);
 
-  int64_t value_;
+  ALIGN8 int64_t value_;
 
   friend class Api;
   friend class SnapshotReader;
 };
+COMPILE_ASSERT(sizeof(RawMint) == 16);
 
 
 class RawBigint : public RawInteger {
@@ -1627,11 +1628,12 @@ class RawBigint : public RawInteger {
 class RawDouble : public RawNumber {
   RAW_HEAP_OBJECT_IMPLEMENTATION(Double);
 
-  double value_;
+  ALIGN8 double value_;
 
   friend class Api;
   friend class SnapshotReader;
 };
+COMPILE_ASSERT(sizeof(RawDouble) == 16);
 
 
 class RawString : public RawInstance {