Implement nan.

BUG=394801

Change-Id: I239b0df708a7cff0fdb53b5417fc13c96947738a
diff --git a/scriptc/rs_cl.rsh b/scriptc/rs_cl.rsh
index bbc8fc5..45d7818 100644
--- a/scriptc/rs_cl.rsh
+++ b/scriptc/rs_cl.rsh
@@ -501,7 +501,7 @@
 extern float __attribute__((overloadable)) modf(float x, float *iret);
 FN_FUNC_FN_PFN(modf);
 
-//extern float __attribute__((overloadable)) nan(uint);
+extern float __attribute__((overloadable)) nan(uint);
 
 /**
  * Return the next floating point number from x towards y.