specific MS adaption

src/maths/fft/fftext.c

@@ -17,6 +17,10 @@
 #include "ngspice/fftext.h"
 #include "ngspice/memory.h"
 
+#ifndef M_PI
+#define M_PI		3.141592653589793238462643383279502884197	// pi
+#endif
+
 #define eq(a,b)  (!strcmp((a), (b)))
 
 // pointers to storage of Utbl's and  BRLow's