Don't merge values for exit block in LSE.

This enables some additional optimizations since exit block doesn't
really merge values.

Test: run-test on host.
Change-Id: I21ed7e0e43a3bc5d9ed2dabfad8462129b904eb7
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index 29c78a1..6672901 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -968,6 +968,7 @@
 
   bool IsSingleGoto() const;
   bool IsSingleReturn() const;
+  bool IsSingleReturnOrReturnVoidAllowingPhis() const;
   bool IsSingleTryBoundary() const;
 
   // Returns true if this block emits nothing but a jump.