Replaced "math.h" by "BLI_math.h" to suppress a warning with regard

to redefinition of M_PI.

source/blender/freestyle/intern/system/FreestyleConfig.h

@@ -32,17 +32,12 @@
 # define CONFIG_H
 
 # include <string>
-# include <math.h>
+# include "BLI_math.h"
 
 using namespace std;
 
 namespace Config {
 
-  // Pi definition
-# ifndef M_PI
-#  define M_PI 3.14159265
-# endif // M_PI
-
   // Directory separators
 # ifdef WIN32
   static const string DIR_SEP("\\");