Use -Werror in external/tremolo

* Suppress non-critical warnings.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: Ibce3b11217d9b03955abb02371a5f0023bb4aa49
diff --git a/Android.bp b/Android.bp
index e9e3f98..c705804 100644
--- a/Android.bp
+++ b/Android.bp
@@ -52,6 +52,9 @@
         "-O2",
         "-D_GNU_SOURCE",
         "-funsigned-char",
+        "-Wall",
+        "-Werror",
+        "-Wno-unused-variable",
     ],
 
     local_include_dirs: ["Tremolo"],