avoid use of private PI definitions

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@61312 15284696-431f-4ddb-bdfa-cd5b030d7da7

imagery/i.aster.toar/main.c

@@ -42,7 +42,7 @@ double gain_aster(int band_number, int gain_code);
 #define KEXO8 66.41
 #define KEXO9 59.83
 
-#define PI 3.1415926
+#define PI M_PI
 
 double rad2ref_aster(double radiance, double doy, double sun_elevation,
 		     double k_exo);

vector/v.lrs/v.lrs.label/main.c

@@ -35,7 +35,7 @@
 #include <grass/glocale.h>
 #include "../lib/lrs.h"
 
-# define PI    3.1415926535897932384626433832795029L
+#define PI M_PI
 
 typedef struct
 {