Yet further adjust degree-based trig functions for more portability.

Buildfarm member cockatiel is still saying that cosd(60) isn't 0.5.
What seems likely is that the subexpression (1.0 - cos(x)) isn't being
rounded to double width before more arithmetic is done on it, so force
that by storing it into a variable.

src/backend/utils/adt/float.c

@@ -2000,7 +2000,9 @@ sind_0_to_30(double x)
 static double
 cosd_0_to_60(double x)
 {
-	return 1.0 - ((1.0 - cos(x * RADIANS_PER_DEGREE)) / one_minus_cos_60) / 2.0;
+	float8		one_minus_cos_x = 1.0 - cos(x * RADIANS_PER_DEGREE);
+
+	return 1.0 - (one_minus_cos_x / one_minus_cos_60) / 2.0;
 }