Add approx_atan and header guards to rs_cl.rsh

Change-Id: Ic58c3d91646b02aff4822e74d3a45d2b9c253912
diff --git a/scriptc/rs_cl.rsh b/scriptc/rs_cl.rsh
index f55f825..ad7e56d 100644
--- a/scriptc/rs_cl.rsh
+++ b/scriptc/rs_cl.rsh
@@ -905,6 +905,10 @@
 _RS_RUNTIME float __attribute__((overloadable)) normalize(float v);
 FN_FUNC_FN(normalize)
 
+
+// New approx API functions
+#if (defined(RS_VERSION) && (RS_VERSION >= 17))
+
 /**
  * Return the approximate reciprocal of a value.
  *
@@ -953,6 +957,17 @@
 _RS_RUNTIME float __attribute__((overloadable)) approx_normalize(float v);
 F_FUNC_FN(approx_normalize)
 
+/**
+ * Compute the approximate arctangent of a value.
+ *
+ * Supports 1,2,3,4 components
+ */
+_RS_RUNTIME float __attribute__((overloadable)) approx_atan(float v);
+FN_FUNC_FN(approx_atan)
+
+#endif  // (defined(RS_VERSION) && (RS_VERSION >= 17))
+
+
 #undef CVT_FUNC
 #undef CVT_FUNC_2
 #undef FN_FUNC_FN