[llvm] [ADT] Fix a bug in EquivalenceClasses::erase (PR #161121)

[Jakub Kuderski via llvm-commits]

================
@@ -108,6 +108,29 @@ TEST(EquivalenceClassesTest, SimpleErase4) {
   EXPECT_FALSE(EqClasses.erase(1));
 }
 
+TEST(EquivalenceClassesTest, EraseKeepsLeaderBit) {
+  EquivalenceClasses<int> EC;
+
+  // Create a set {1, 2} where 1 is the leader.
+  EC.unionSets(1, 2);
+
+  // Verify initial state
----------------
kuhar wrote:

```suggestion
  // Verify initial state.
```

https://github.com/llvm/llvm-project/pull/161121