[llvm] [SSAUpdater] Don't use large SmallSets for IDFcalc (PR #97823)

[Jakub Kuderski via llvm-commits]

================
@@ -111,17 +112,22 @@ class SmallPtrSetImplBase : public DebugEpochBase {
 
   void reserve(size_type NumEntries) {
     incrementEpoch();
+    // Do nothing if we're given zero as a reservation size.
+    if (!NumEntries)
----------------
kuhar wrote:

```suggestion
    if (NumEntries == 0)
```

https://github.com/llvm/llvm-project/pull/97823