Add math routines with defined wrapping behavior for the interpreter.

Add a RSUB_INT_LIT16 instruction alias to make instruction opcode switch
statements easier to read.

Change-Id: I3bac07c9518665abf0b05b5c3105a90be22f780a
diff --git a/runtime/dex_instruction.h b/runtime/dex_instruction.h
index b913220..72802e4 100644
--- a/runtime/dex_instruction.h
+++ b/runtime/dex_instruction.h
@@ -88,6 +88,7 @@
     DEX_INSTRUCTION_LIST(INSTRUCTION_ENUM)
 #undef DEX_INSTRUCTION_LIST
 #undef INSTRUCTION_ENUM
+    RSUB_INT_LIT16 = RSUB_INT,
   };
 
   enum Format {