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/libc/BUILD b/aos/common/libc/BUILD
index e2a87cb..74a4c70 100644
--- a/aos/common/libc/BUILD
+++ b/aos/common/libc/BUILD
@@ -1,68 +1,71 @@
-package(default_visibility = ['//visibility:public'])
+package(default_visibility = ["//visibility:public"])
 
 cc_library(
-  name = 'aos_strsignal',
-  srcs = [
-    'aos_strsignal.cc',
-  ],
-  hdrs = [
-    'aos_strsignal.h',
-  ],
-  deps = [
-    '//aos/common/logging',
-  ],
+    name = "aos_strsignal",
+    srcs = [
+        "aos_strsignal.cc",
+    ],
+    hdrs = [
+        "aos_strsignal.h",
+    ],
+    deps = [
+        "//aos/common/logging",
+    ],
 )
 
 cc_test(
-  name = 'aos_strsignal_test',
-  srcs = [
-    'aos_strsignal_test.cc',
-  ],
-  deps = [
-    ':aos_strsignal',
-    '//aos/testing:googletest',
-    '//aos/common/logging',
-  ],
+    name = "aos_strsignal_test",
+    srcs = [
+        "aos_strsignal_test.cc",
+    ],
+    deps = [
+        ":aos_strsignal",
+        "//aos/common/logging",
+        "//aos/testing:googletest",
+    ],
 )
 
 cc_library(
-  name = 'dirname',
-  srcs = [
-    'dirname.cc',
-  ],
-  hdrs = [
-    'dirname.h',
-  ],
+    name = "dirname",
+    srcs = [
+        "dirname.cc",
+    ],
+    hdrs = [
+        "dirname.h",
+    ],
 )
 
 cc_test(
-  name = 'dirname_test',
-  srcs = [
-    'dirname_test.cc',
-  ],
-  deps = [
-    ':dirname',
-    '//aos/testing:googletest',
-  ],
+    name = "dirname_test",
+    srcs = [
+        "dirname_test.cc",
+    ],
+    deps = [
+        ":dirname",
+        "//aos/testing:googletest",
+    ],
 )
 
 cc_library(
-  name = 'aos_strerror',
-  srcs = [
-    'aos_strerror.cc',
-  ],
-  hdrs = [
-    'aos_strerror.h',
-  ],
+    name = "aos_strerror",
+    srcs = [
+        "aos_strerror.cc",
+    ],
+    hdrs = [
+        "aos_strerror.h",
+    ],
+    compatible_with = [
+        "//tools:armhf-debian",
+    ],
 )
 
 cc_test(
-  name = 'aos_strerror_test',
-  srcs = [
-    'aos_strerror_test.cc',
-  ],
-  deps = [
-    ':aos_strerror',
-    '//aos/testing:googletest',
-  ],
+    name = "aos_strerror_test",
+    srcs = [
+        "aos_strerror_test.cc",
+    ],
+    deps = [
+        ":aos_strerror",
+        "//aos/testing:googletest",
+    ],
 )