libvpx: Pull from upstream

source/libvpx/vp8/common/postproc.c

Index: source/libvpx/vp8/common/postproc.c
diff --git a/source/libvpx/vp8/common/postproc.c b/source/libvpx/vp8/common/postproc.c
index a4e6ae170c961bd240077fd8274978cb1db848fe..322b61383b5bae2229d0ea478044c8df7a25ab13 100644
--- a/source/libvpx/vp8/common/postproc.c
+++ b/source/libvpx/vp8/common/postproc.c
@@ -675,6 +675,7 @@ void vp8_blend_b_c (unsigned char *y, unsigned char *u, unsigned char *v,
     }
 }
 
+#if CONFIG_POSTPROC_VISUALIZER
 static void constrain_line (int x_0, int *x_1, int y_0, int *y_1, int width, int height)
 {
     int dx;
@@ -717,6 +718,7 @@ static void constrain_line (int x_0, int *x_1, int y_0, int *y_1, int width, int
             *x_1 = ((0-y_0)*dx)/dy + x_0;
     }
 }
+#endif  // CONFIG_POSTPROC_VISUALIZER
 
 #if CONFIG_POSTPROC
 int vp8_post_proc_frame(VP8_COMMON *oci, YV12_BUFFER_CONFIG *dest, vp8_ppflags_t *ppflags)