Change Function::getIntrinsicID() to return an Intrinsic::ID.  NFC.

Now that Intrinsic::ID is a typed enum, we can forward declare it and so return it from this method.

This updates all users which were either using an unsigned to store it, or had a now unnecessary cast.

llvm-svn: 237810
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 4fe7bfb..85303d2 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5450,7 +5450,7 @@
             return;
         }
       }
-      if (unsigned IID = F->getIntrinsicID()) {
+      if (Intrinsic::ID IID = F->getIntrinsicID()) {
         RenameFn = visitIntrinsicCall(I, IID);
         if (!RenameFn)
           return;