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/cmds/am/Android.bp b/cmds/am/Android.bp
index 7eb4edf..bb16df1 100644
--- a/cmds/am/Android.bp
+++ b/cmds/am/Android.bp
@@ -4,6 +4,7 @@
 cc_library_host_static {
     name: "libinstrumentation",
     srcs: ["**/*.proto"],
+    cflags: ["-Wall", "-Werror"],
     proto: {
         type: "full",
         export_proto_headers: true,