Fix definition of M_PI in geohash_helper.c.

Without the right feature macros M_PI is not defined in math.h.

src/geohash_helper.c

@@ -34,7 +34,9 @@
  * https://github.com/yinqiwen/ardb/blob/d42503/src/geo/geohash_helper.cpp
  */
 
+#include "fmacros.h"
 #include "geohash_helper.h"
+#include <math.h>
 
 #define D_R (M_PI / 180.0)
 #define R_MAJOR 6378137.0

src/geohash_helper.h

@@ -32,7 +32,6 @@
 #ifndef GEOHASH_HELPER_HPP_
 #define GEOHASH_HELPER_HPP_
 
-#include <math.h>
 #include "geohash.h"
 
 #define GZERO(s) s.bits = s.step = 0;