Complain about attempts to use 'protected' visibility on targets
like Darwin that don't support it.  We should also complain about
invalid -fvisibility=protected, but that information doesn't seem
to exist at the most appropriate time, so I've left a FIXME behind.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149186 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index a189155..e9bb303 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -1792,6 +1792,7 @@
   else if (Vis == "hidden")
     Opts.setVisibilityMode(HiddenVisibility);
   else if (Vis == "protected")
+    // FIXME: diagnose if target does not support protected visibility
     Opts.setVisibilityMode(ProtectedVisibility);
   else
     Diags.Report(diag::err_drv_invalid_value)