Opaque types didn't work if llvm_is_multithreaded().

AlwaysOpaqueTy is always NULL at this point, and it causes an assertion failure.
Fix it by using the just constructed tmp instead.

llvm-svn: 80780

llvm/lib/VMCore/Type.cpp

@@ -492,7 +492,7 @@ void DerivedType::dropAllTypeUses() {
         tmp = AlwaysOpaqueTy;
         if (!tmp) {
           tmp = OpaqueType::get(getContext());
-          PATypeHolder* tmp2 = new PATypeHolder(AlwaysOpaqueTy);
+          PATypeHolder* tmp2 = new PATypeHolder(tmp);
           sys::MemoryFence();
           AlwaysOpaqueTy = tmp;
           Holder = tmp2;