libcutils: build tests with -Wall -Wextra -Werror

Test: mmm system/core/libcutils/tests

Change-Id: Iede18a008df5834b8ecedd6019c4444150748f68
Signed-off-by: Greg Hackmann <ghackmann@google.com>
diff --git a/libcutils/tests/Android.bp b/libcutils/tests/Android.bp
index 0b0dc09..718d76b 100644
--- a/libcutils/tests/Android.bp
+++ b/libcutils/tests/Android.bp
@@ -46,6 +46,12 @@
             suffix: "64",
         },
     },
+
+    cflags: [
+        "-Wall",
+        "-Wextra",
+        "-Werror",
+    ],
 }
 
 test_libraries = [