Use -Werror in frameworks/native/opengl/libs

* Suppress unused variable warnings.
* Keep existing warnings as no-error, to fix later.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I2e329715ffadcc14909e19df9b26be515f2a0748
diff --git a/opengl/libs/Android.bp b/opengl/libs/Android.bp
index 59424cd..63c79de 100644
--- a/opengl/libs/Android.bp
+++ b/opengl/libs/Android.bp
@@ -3,6 +3,7 @@
     name: "libETC1",
     srcs: ["ETC1/etc1.cpp"],
     host_supported: true,
+    cflags: ["-Wall", "-Werror"],
 
     target: {
         android: {
@@ -56,6 +57,9 @@
         "-DGL_GLEXT_PROTOTYPES",
         "-DEGL_EGLEXT_PROTOTYPES",
         "-fvisibility=hidden",
+        "-Wall",
+        "-Werror",
+        "-Wno-unused-variable",
     ],
     shared_libs: [
         // ***** DO NOT ADD NEW DEPENDENCIES HERE *****
@@ -86,6 +90,11 @@
     defaults: ["gl_libs_defaults"],
     cflags: [
         "-DLOG_TAG=\"libEGL\"",
+        "-Wall",
+        "-Werror",
+        "-Wno-error=deprecated-register",
+        "-Wno-error=unknown-attributes",
+        "-Wno-unused-variable",
     ],
     shared_libs: [
         // ***** DO NOT ADD NEW DEPENDENCIES HERE *****