[escher] Build escher examples on Linux buildbots.

TEST=CQ

IN-901 #done

Change-Id: I713aba5855668940588fec4171a17da00a1f95db
diff --git a/public/lib/escher/test/BUILD.gn b/public/lib/escher/test/BUILD.gn
index 771195b..8646452 100644
--- a/public/lib/escher/test/BUILD.gn
+++ b/public/lib/escher/test/BUILD.gn
@@ -72,6 +72,7 @@
     ]
 
     deps = [
+      ":force_waterfall_to_build_on_host",
       ":gtest_escher",
       "base:base_unittests",
       "//garnet/public/lib/fxl",
@@ -146,3 +147,10 @@
     "gtest_escher.h",
   ]
 }
+
+group("force_waterfall_to_build_on_host") {
+  deps = [
+    "//garnet/examples/escher/waterfall($host_toolchain)",
+    "//garnet/examples/escher/waterfall2($host_toolchain)"
+  ]
+}
\ No newline at end of file