Ensure stack maps are 4 byte aligned.

With the recent move to gcc 4.9, we are hitting alignment
SIGBUS on ARM. The reason is that gcc will optimize two consecutive
32bits loads into one 64bits load, and the instruction (ldrd)
will fail if the data is not aligned.

Also removed the emission of mapping table when a method is optimized.
The information can be found in the StackMap itself.

Change-Id: Icf79406c18a3f4db3c05d52fc2c0dd2e35bf0f8f
diff --git a/compiler/oat_writer.cc b/compiler/oat_writer.cc
index 8a7abb4..6bb526c 100644
--- a/compiler/oat_writer.cc
+++ b/compiler/oat_writer.cc
@@ -530,7 +530,7 @@
 
 struct OatWriter::MappingTableDataAccess {
   static const std::vector<uint8_t>* GetData(const CompiledMethod* compiled_method) ALWAYS_INLINE {
-    return &compiled_method->GetMappingTable();
+    return compiled_method->GetMappingTable();
   }
 
   static uint32_t GetOffset(OatClass* oat_class, size_t method_offsets_index) ALWAYS_INLINE {