Use -Werror in external/libavc

* Suppress unused-variable warnings.
* Keep constant-conversion warnings.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: Id46435816c0d671c9e03c5297810596df596c7f2

Android.bp

@@ -4,6 +4,9 @@ cc_library_static {
     cflags: [
         "-fPIC",
         "-O3",
+        "-Wall",
+        "-Werror",
+        "-Wno-unused-variable",
     ],
 
     export_include_dirs: [
@@ -238,6 +241,9 @@ cc_library_static {
         "-fPIC",
 
         "-O3",
+        "-Wall",
+        "-Werror",
+        "-Wno-error=constant-conversion",
     ],
 
     export_include_dirs: [

test/Android.bp

@@ -7,6 +7,8 @@ cc_test {
         "-DARM",
         "-DMD5_DISABLE",
         "-fPIC",
+        "-Wall",
+        "-Werror",
     ],
     local_include_dirs: [
         "decoder/",
@@ -26,6 +28,9 @@ cc_test {
         "-DMD5_DISABLE",
         "-fPIC",
         "-pie",
+        "-Wall",
+        "-Werror",
+        "-Wno-unused-variable",
     ],
     local_include_dirs: [
         "encoder/",