Use a trivial comdat for C++ tables.

This produces comdats for vtables, typeinfo, typeinfo names, and vtts.

When combined with llvm not producing implicit comdats, not doing this would
cause code bloat on ELF and link errors on COFF.

llvm-svn: 226227

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1828,7 +1828,10 @@ CodeGenModule::CreateOrReplaceCXXRuntimeVariable(StringRef Name,
     
     OldGV->eraseFromParent();
   }
-  
+
+  if (supportsCOMDAT() && GV->isWeakForLinker())
+    GV->setComdat(TheModule.getOrInsertComdat(GV->getName()));
+
   return GV;
 }