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/linux_code/BUILD b/aos/linux_code/BUILD
index 3884130..b572a25 100644
--- a/aos/linux_code/BUILD
+++ b/aos/linux_code/BUILD
@@ -17,6 +17,9 @@
     hdrs = [
         "queue-tmpl.h",
     ],
+    compatible_with = [
+        "//tools:armhf-debian",
+    ],
     visibility = ["//aos/common:__pkg__"],
 )
 
@@ -28,6 +31,9 @@
     hdrs = [
         "complex_thread_local.h",
     ],
+    compatible_with = [
+        "//tools:armhf-debian",
+    ],
     linkopts = [
         "-lpthread",
     ],
@@ -58,6 +64,9 @@
     hdrs = [
         "init.h",
     ],
+    compatible_with = [
+        "//tools:armhf-debian",
+    ],
     deps = [
         "//aos/common:die",
         "//aos/common/logging:implementations",
@@ -73,6 +82,9 @@
     hdrs = [
         "configuration.h",
     ],
+    compatible_with = [
+        "//tools:armhf-debian",
+    ],
     deps = [
         "//aos:once",
         "//aos/common:unique_malloc_ptr",