Use -Werror in frameworks/native/libs/vr

* Suppress/fix warnings of unused variable, parameter,
  private-field, and function.
* Fix warnings about typedef missing declarator.
* Use -Wno-error to keep existing warnings, to fix later.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: Ifb82fcd76fcb5d9c9d9f017f2541581661493bd5
diff --git a/libs/vr/libbufferhub/Android.bp b/libs/vr/libbufferhub/Android.bp
index 17725f8..2819fe9 100644
--- a/libs/vr/libbufferhub/Android.bp
+++ b/libs/vr/libbufferhub/Android.bp
@@ -42,6 +42,9 @@
         "-DLOG_TAG=\"libbufferhub\"",
         "-DTRACE=0",
         "-DATRACE_TAG=ATRACE_TAG_GRAPHICS",
+        "-Wall",
+        "-Werror",
+        "-Wno-error=sign-compare", // to fix later
     ],
     export_include_dirs: localIncludeFiles,
     static_libs: staticLibraries,
@@ -55,5 +58,10 @@
     static_libs: ["libbufferhub"] + staticLibraries,
     shared_libs: sharedLibraries,
     name: "bufferhub_tests",
+    cflags: [
+        "-Wall",
+        "-Werror",
+        "-Wno-error=sign-compare", // to fix later
+    ],
 }