define M_PI if it's not, eg. if compiling with -std=c99

Author: sleepybishop

src/denoise.c

@@ -29,6 +29,10 @@
 #include "config.h"
 #endif
 
+#ifndef M_PI
+#define M_PI (3.14159265358979323846)
+#endif
+
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>