avfilter/vf_gblur: add missing preprocessor check

Fixes compilation on x86_32
Signed-off-by: James Almer <jamrial@gmail.com>

libavfilter/x86/vf_gblur_init.c

@@ -17,6 +17,8 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include "config.h"
+
 #include "libavutil/attributes.h"
 #include "libavutil/cpu.h"
 #include "libavutil/x86/cpu.h"
@@ -27,10 +29,12 @@ void ff_horiz_slice_avx2(float *ptr, int width, int height, int steps, float nu,
 
 av_cold void ff_gblur_init_x86(GBlurContext *s)
 {
+#if ARCH_X86_64
     int cpu_flags = av_get_cpu_flags();
 
     if (EXTERNAL_SSE4(cpu_flags))
         s->horiz_slice = ff_horiz_slice_sse4;
     if (EXTERNAL_AVX2(cpu_flags))
         s->horiz_slice = ff_horiz_slice_avx2;
+#endif
 }