Use -Werror in external/fmtlib am: 5dd1ef0309 am: a12d391b4e
am: 0835801d27

Change-Id: I182937b70123ce5cd58e0fd9f17a950d715d929f
diff --git a/Android.bp b/Android.bp
index e8f4b3a..65a7545 100644
--- a/Android.bp
+++ b/Android.bp
@@ -4,6 +4,8 @@
     cflags: [
         "-std=c++11",
         "-fno-exceptions",
+        "-Wall",
+        "-Werror",
     ],
     sanitize: {
         misc_undefined: ["integer"],