Fix-forward build error from #132489

Replace deprecated use of getDeclaration that was added in #132489

llvm/lib/IR/AutoUpgrade.cpp:1480:26: error: 'getDeclaration' is deprecated: Use getOrInsertDeclaration instead [-Werror,-Wdeprecated-declarations]
 1480 |       NewFn = Intrinsic::getDeclaration(
      |                          ^~~~~~~~~~~~~~
      |                          getOrInsertDeclaration

Author: thurstond

llvm/lib/IR/AutoUpgrade.cpp

@@ -1477,7 +1477,7 @@ static bool upgradeIntrinsicFunction1(Function *F, Function *&NewFn,
 
   case 't':
     if (Name == "thread.pointer") {
-      NewFn = Intrinsic::getDeclaration(
+      NewFn = Intrinsic::getOrInsertDeclaration(
           F->getParent(), Intrinsic::thread_pointer, F->getReturnType());
       return true;
     }