NAN is not always defined in math.h, so using Py_NAN

Author: realead

pandas/_libs/src/klib/khash_python.h

@@ -1,5 +1,4 @@
 #include <string.h>
-#include <math.h>
 #include <Python.h>
 
 #include "khash.h"
@@ -31,7 +30,7 @@ khint64_t PANDAS_INLINE asint64(double key) {
 
 // correct for all
 #define kh_float64_hash_func(key) ((key) != (key) ?                       \
-                                   kh_float64_hash_func_NAN(NAN) :        \
+                                   kh_float64_hash_func_NAN(Py_NAN) :     \
                                    kh_float64_hash_func_NAN(key))
 
 #define kh_float64_hash_equal(a, b) ((a) == (b) || ((b) != (b) && (a) != (a)))