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/math/tests/Android.bp b/libs/math/tests/Android.bp
index 0ed24a2..0184f56 100644
--- a/libs/math/tests/Android.bp
+++ b/libs/math/tests/Android.bp
@@ -18,22 +18,26 @@
     name: "vec_test",
     srcs: ["vec_test.cpp"],
     static_libs: ["libmath"],
+    cflags: ["-Wall", "-Werror"],
 }
 
 cc_test {
     name: "mat_test",
     srcs: ["mat_test.cpp"],
     static_libs: ["libmath"],
+    cflags: ["-Wall", "-Werror"],
 }
 
 cc_test {
     name: "half_test",
     srcs: ["half_test.cpp"],
     static_libs: ["libmath"],
+    cflags: ["-Wall", "-Werror"],
 }
 
 cc_test {
     name: "quat_test",
     srcs: ["quat_test.cpp"],
     static_libs: ["libmath"],
+    cflags: ["-Wall", "-Werror"],
 }