Use -Werror in frameworks/base

* Fix unused variable and return value warnings.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I890e65a20848d00559ba5a4f9691be1347b456af
diff --git a/Android.bp b/Android.bp
index b83c63f..cf9610d 100644
--- a/Android.bp
+++ b/Android.bp
@@ -34,6 +34,11 @@
         include_dirs: ["external/protobuf/src"],
     },
 
+    cflags: [
+        "-Wall",
+        "-Werror",
+        "-Wno-unused-parameter",
+    ],
     target: {
         host: {
             proto: {