Use -Werror in bionic

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: Ic68141a5c50880c485646e38349f94b866267bd9
diff --git a/tests/libs/Android.bp b/tests/libs/Android.bp
index aa4d0dd..858f2b1 100644
--- a/tests/libs/Android.bp
+++ b/tests/libs/Android.bp
@@ -17,6 +17,10 @@
 cc_defaults {
     name: "bionic_testlib_defaults",
     host_supported: true,
+    cflags: [
+        "-Wall",
+        "-Werror",
+    ],
     ldflags: [
         "-Wl,--rpath,${ORIGIN}",
         "-Wl,--enable-new-dtags",