Bug 1932772 - part14 : Suppress warnings in ffvpx. r=media-playback-reviewers,chunmin

Differential Revision: https://phabricator.services.mozilla.com/D230732

media/ffvpx/ffvpxcommon.mozbuild

@@ -62,6 +62,14 @@ if CONFIG['CC_TYPE'] == 'clang-cl':
     LOCAL_INCLUDES += ['/media/ffvpx/compat/atomics/win32']
 DEFINES['HAVE_AV_CONFIG_H'] = True
 
+if CONFIG['CC_TYPE'] == 'clang':
+  CXXFLAGS += [
+      '-Wsometimes-uninitialized',
+      '-Wunreachable-code-return',
+      '-Wunreachable-code',
+      '-Wunused-const-variable',
+  ]
+
 if CONFIG['MOZ_DEBUG']:
     # Enable all assertions in debug builds.
     DEFINES['ASSERT_LEVEL'] = 2