Make :dot-graphs genrule quiet 

The output of `which dot` is not a helpful diagnostic
message; so discard it in the test whether dot is installed
on the given system.

--
Change-Id: Ic6597a517cafe99796a9c109e3844c1fa56c8c97
Reviewed-on: https://cr.bazel.build/9120
PiperOrigin-RevId: 149002252
MOS_MIGRATED_REVID=149002252

site/BUILD

diff --git a/site/BUILD b/site/BUILD
index 130d159..acada35 100644
--- a/site/BUILD
+++ b/site/BUILD
@@ -106,7 +106,7 @@
 tmpdir=$$(mktemp -d)
 for f in $(SRCS); do
     mkdir -p $$tmpdir/$$(dirname $$f)
-    if which dot; then
+    if which dot > /dev/null; then
       $(location //scripts/docs:generate_dot_graphs) < $$f > $$tmpdir/$$f
     else
       cp $$f $$tmpdir/$$f