Use the downloaded clang when building for armhf-debian

This makes it work on a barebones Stretch installation.

Also add building for this CPU to the CI script so we know it keeps
working, which means marking everything that's supposed to work
appropriately.

Change-Id: Ic050ce20eae45c6b23e0e42dddb24db3ebc70b84
diff --git a/aos/common/controls/BUILD b/aos/common/controls/BUILD
index 46b5f24..7ca2e60 100644
--- a/aos/common/controls/BUILD
+++ b/aos/common/controls/BUILD
@@ -78,6 +78,9 @@
     srcs = [
         "control_loops.q",
     ],
+    compatible_with = [
+        "//tools:armhf-debian",
+    ],
 )
 
 cc_library(