Use -Werror in frameworks/native/libs

* Suppress unused-variable and user-defined warnings.
* Keep sign-compare warnings to fix later.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I6eee1532aa22c92ed19515ad5574734d1016d967
diff --git a/libs/input/tests/Android.bp b/libs/input/tests/Android.bp
index 029a420..0028655 100644
--- a/libs/input/tests/Android.bp
+++ b/libs/input/tests/Android.bp
@@ -7,6 +7,12 @@
         "InputEvent_test.cpp",
         "InputPublisherAndConsumer_test.cpp",
     ],
+    cflags: [
+        "-Wall",
+        "-Werror",
+        "-Wno-error=sign-compare", // to fix later
+        "-Wno-unused-variable",
+    ],
     shared_libs: [
         "libinput",
         "libcutils",
@@ -24,5 +30,7 @@
     srcs: ["StructLayout_test.cpp"],
     cflags: [
         "-O0",
+        "-Wall",
+        "-Werror",
     ],
 }