vips_gaussblur: remove dependency on libmath

remove ceil() on call to vips_gaussblur, simply cast to int

vips.h

@@ -16,9 +16,6 @@
  */
 
 #if (VIPS_MAJOR_VERSION == 7 && VIPS_MINOR_VERSION < 41)
-/* we need math.h for ceil() in vips_gaussblur_bridge */
-#include <math.h>
-
 #define VIPS_ANGLE_D0 VIPS_ANGLE_0
 #define VIPS_ANGLE_D90 VIPS_ANGLE_90
 #define VIPS_ANGLE_D180 VIPS_ANGLE_180
@@ -328,7 +325,7 @@ vips_watermark(VipsImage *in, VipsImage **out, WatermarkTextOptions *to, Waterma
 int
 vips_gaussblur_bridge(VipsImage *in, VipsImage **out, double sigma, double min_ampl) {
 #if (VIPS_MAJOR_VERSION == 7 && VIPS_MINOR_VERSION < 41)
-	return vips_gaussblur(in, out, ceil(sigma), NULL);
+	return vips_gaussblur(in, out, (int) sigma, NULL);
 #else
 	return vips_gaussblur(in, out, sigma, NULL, "min_ampl", min_ampl, NULL);
 #endif