Use -Werror in frameworks/native/services/inputflinger

* Fix/suppress unused-* warnings.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: If1dd59ea4ee8ce51f7b58ae4581531df301c68a8
diff --git a/services/inputflinger/Android.bp b/services/inputflinger/Android.bp
index 4fd98e2..238cba3 100644
--- a/services/inputflinger/Android.bp
+++ b/services/inputflinger/Android.bp
@@ -37,6 +37,9 @@
     ],
 
     cflags: [
+        "-Wall",
+        "-Wextra",
+        "-Werror",
         "-Wno-unused-parameter",
         // TODO: Move inputflinger to its own process and mark it hidden
         //-fvisibility=hidden