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/frc971/BUILD b/frc971/BUILD
index 563f05e..b9987a4 100644
--- a/frc971/BUILD
+++ b/frc971/BUILD
@@ -7,7 +7,9 @@
     hdrs = [
         "shifter_hall_effect.h",
     ],
-    compatible_with = mcu_cpus,
+    compatible_with = mcu_cpus + [
+        "//tools:armhf-debian",
+    ],
 )
 
 cc_library(
@@ -15,6 +17,9 @@
     hdrs = [
         "constants.h",
     ],
+    compatible_with = [
+        "//tools:armhf-debian",
+    ],
 )
 
 py_library(
diff --git a/frc971/control_loops/BUILD b/frc971/control_loops/BUILD
index 7c39a85..16673df 100644
--- a/frc971/control_loops/BUILD
+++ b/frc971/control_loops/BUILD
@@ -44,6 +44,9 @@
     srcs = [
         "control_loops.q",
     ],
+    compatible_with = [
+        "//tools:armhf-debian",
+    ],
 )
 
 cc_test(
@@ -142,6 +145,9 @@
     hdrs = [
         "state_feedback_loop.h",
     ],
+    compatible_with = [
+        "//tools:armhf-debian",
+    ],
     deps = [
         "//aos/common:macros",
         "//aos/common/logging",
diff --git a/frc971/control_loops/drivetrain/BUILD b/frc971/control_loops/drivetrain/BUILD
index 90385e0..64d1d9d 100644
--- a/frc971/control_loops/drivetrain/BUILD
+++ b/frc971/control_loops/drivetrain/BUILD
@@ -21,6 +21,9 @@
     srcs = [
         "drivetrain.q",
     ],
+    compatible_with = [
+        "//tools:armhf-debian",
+    ],
     deps = [
         "//aos/common/controls:control_loop_queues",
         "//frc971/control_loops:queues",