Revert my available_externally vtables experiment. It's breaking the LLVM-with-Clang build with linker errors that I have yet to investigate.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@92822 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGVtable.cpp b/lib/CodeGen/CGVtable.cpp
index d89c669..2cb877b 100644
--- a/lib/CodeGen/CGVtable.cpp
+++ b/lib/CodeGen/CGVtable.cpp
@@ -1506,7 +1506,10 @@
       break;
 
     case TSK_ExplicitInstantiationDeclaration:
-      Linkage = llvm::GlobalVariable::AvailableExternallyLinkage;
+      // FIXME: Use available_externally linkage. However, this currently
+      // breaks LLVM's build due to undefined symbols.
+      //      Linkage = llvm::GlobalVariable::AvailableExternallyLinkage;
+      Linkage = llvm::GlobalVariable::WeakODRLinkage;
       break;
     }
   }
@@ -1523,7 +1526,9 @@
       break;
 
     case TSK_ExplicitInstantiationDeclaration:
-      Linkage = llvm::GlobalVariable::AvailableExternallyLinkage;
+      // FIXME: Use available_externally linkage. However, this currently
+      // breaks LLVM's build due to undefined symbols.
+      // Linkage = llvm::GlobalVariable::AvailableExternallyLinkage;
       break;
     }
   }