Store the instruction set in the oat header, and use it in oatdump.

Change-Id: I5cc4b853c3ebf1efcc1feb14ce05c97ceabe2c3e
diff --git a/src/oat_writer.h b/src/oat_writer.h
index abb1f2e..cdc061f 100644
--- a/src/oat_writer.h
+++ b/src/oat_writer.h
@@ -73,7 +73,7 @@
             const Compiler& compiler);
   ~OatWriter();
 
-  size_t InitOatHeader();
+  size_t InitOatHeader(InstructionSet instruction_set);
   size_t InitOatDexFiles(size_t offset);
   size_t InitDexFiles(size_t offset);
   size_t InitOatClasses(size_t offset);