Use M_PI instead of PI.

src/libespeak-ng/klatt.c

 
 	fla = (double)kt_globals.f0_flutter / 50;
 	flb = (double)kt_globals.original_f0 / 100;
-	flc = sin(PI*12.7*time_count); // because we are calling flutter() more frequently, every 2.9mS
+	flc = sin(M_PI*12.7*time_count); // because we are calling flutter() more frequently, every 2.9mS
-	fld = sin(PI*7.1*time_count);
+	fld = sin(M_PI*7.1*time_count);
-	fle = sin(PI*4.7*time_count);
+	fle = sin(M_PI*4.7*time_count);
 	delta_f0 =  fla * flb * (flc + fld + fle) * 10;
 	frame->F0hz10 = frame->F0hz10 + (long)delta_f0;
 	time_count++;
 		// Full reset
 		kt_globals.FLPhz = (950 * kt_globals.samrate) / 10000;
 		kt_globals.BLPhz = (630 * kt_globals.samrate) / 10000;
-		kt_globals.minus_pi_t = -PI / kt_globals.samrate;
+		kt_globals.minus_pi_t = -M_PI / kt_globals.samrate;
 		kt_globals.two_pi_t = -2.0 * kt_globals.minus_pi_t;
 		setabc(kt_globals.FLPhz, kt_globals.BLPhz, &(kt_globals.rsn[RLP]));
 	}

src/libespeak-ng/klatt.h

 #define SAMPLED          3
 #define SAMPLED2         4
 
-#define PI               3.1415927
-
-
 /* typedef's that need to be exported */
 
 typedef long flag;

src/libespeak-ng/wavegen.c

 
 #include "sintab.h"
 
-#define PI  3.1415927
-#define PI2 6.283185307
 #define N_WAV_BUF   10
 
 voice_t *wvoice;
 		// wavemult table has preset values for 22050 Hz, we only need to
 		// recalculate them if we have a different sample rate
 		for (ix = 0; ix < wavemult_max; ix++) {
-			x = 127*(1.0 - cos(PI2*ix/wavemult_max));
+			x = 127*(1.0 - cos((M_PI*2)*ix/wavemult_max));
 			wavemult[ix] = (int)x;
 		}
 	}
 {
 	int ix;
 
-	minus_pi_t = -PI / samplerate;
+	minus_pi_t = -M_PI / samplerate;
 	two_pi_t = -2.0 * minus_pi_t;
 
 	for (ix = 0; ix < N_PEAKS; ix++)