Add a flag to enable ConcurrentValue inference for public structs/enums.

lib/Frontend/CompilerInvocation.cpp

@@ -385,6 +385,10 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
 
   Opts.EnableExperimentalConcurrency |=
     Args.hasArg(OPT_enable_experimental_concurrency);
+  Opts.EnableInferPublicConcurrentValue |=
+    Args.hasFlag(OPT_enable_infer_public_concurrent_value,
+                 OPT_disable_infer_public_concurrent_value,
+                 false);
   Opts.EnableExperimentalFlowSensitiveConcurrentCaptures |=
     Args.hasArg(OPT_enable_experimental_flow_sensitive_concurrent_captures);