Remove constant moves after emitting them in parallel resolver.

This fixes the case where a constant move requires a scratch
register. Note that there is no backend that needs this for now,
but X86 might with the move to hard float.

Change-Id: I37f6b8961b48f2cf6fbc0cd281e70d58466d018e
diff --git a/compiler/optimizing/parallel_move_resolver.h b/compiler/optimizing/parallel_move_resolver.h
index 309425e..7ec1dd2 100644
--- a/compiler/optimizing/parallel_move_resolver.h
+++ b/compiler/optimizing/parallel_move_resolver.h
@@ -58,6 +58,9 @@
   };
 
   bool IsScratchLocation(Location loc);
+
+  // Allocate a scratch register for performing a move. The method will try to use
+  // a register that is the destination of a move, but that move has not been emitted yet.
   int AllocateScratchRegister(int blocked, int if_scratch, int register_count, bool* spilled);
 
   // Emit a move.