lib/msun: cpow{,f,l}(CMLX(0.0, 0.0)) should return 1.0

PR:	289447
MFC after:	1 week

lib/msun/src/s_cpow.c

@@ -58,7 +58,10 @@ cpow(double complex a, double complex z)
 	y = cimag (z);
 	absa = cabs (a);
 	if (absa == 0.0) {
-		return (CMPLX(0.0, 0.0));
+		if (x == 0 && y == 0)
+		    return (CMPLX(1., 0.));
+		else
+		    return (CMPLX(0., 0.));
 	}
 	arga = carg (a);
 	r = pow (absa, x);

lib/msun/src/s_cpowf.c

@@ -57,7 +57,10 @@ cpowf(float complex a, float complex z)
 	y = cimagf(z);
 	absa = cabsf (a);
 	if (absa == 0.0f) {
-		return (CMPLXF(0.0f, 0.0f));
+		if (x == 0 && y == 0)
+		    return (CMPLXF(1.f, 0.f));
+		else
+		    return (CMPLXF(0.f, 0.f));
 	}
 	arga = cargf (a);
 	r = powf (absa, x);

lib/msun/src/s_cpowl.c

@@ -57,7 +57,10 @@ cpowl(long double complex a, long double complex z)
 	y = cimagl(z);
 	absa = cabsl(a);
 	if (absa == 0.0L) {
-		return (CMPLXL(0.0L, 0.0L));
+		if (x == 0 && y == 0)
+		    return (CMPLXL(1.L, 0.L));
+		else
+		    return (CMPLXL(0.L, 0.L));
 	}
 	arga = cargl(a);
 	r = powl(absa, x);