Omit private_extern declarations of extern symbols; followup to
r124468.  Patch by Rafael Avila de Espindola!

llvm-svn: 126297
diff --git a/llvm/lib/MC/MCAsmInfoDarwin.cpp b/llvm/lib/MC/MCAsmInfoDarwin.cpp
index 13776f0..526ad0d 100644
--- a/llvm/lib/MC/MCAsmInfoDarwin.cpp
+++ b/llvm/lib/MC/MCAsmInfoDarwin.cpp
@@ -45,6 +45,7 @@
   HasAggressiveSymbolFolding = false;
 
   HiddenVisibilityAttr = MCSA_PrivateExtern;
+  HiddenDeclarationVisibilityAttr = MCSA_Invalid;
   // Doesn't support protected visibility.
   ProtectedVisibilityAttr = MCSA_Global;