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: Iae96af3f6a17623befe73a9db2c81275fee44fa6
diff --git a/libs/vr/libdvr/Android.bp b/libs/vr/libdvr/Android.bp
index 7fe9825..0d23b62 100644
--- a/libs/vr/libdvr/Android.bp
+++ b/libs/vr/libdvr/Android.bp
@@ -22,6 +22,8 @@
 cflags = [
     "-DLOG_TAG=\"libdvr\"",
     "-DTRACE=0",
+    "-Wall",
+    "-Werror",
 ]
 
 srcs = [