[ADT] Teach set_intersect to erase with iterators (#99569)

Summary:
Without this patch, we erase an element in S1 by value even though we
have an interator pointing to it.  This patch tries to use erase(iter)
to avoid redundant lookups.

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Differential Revision: https://phabricator.intern.facebook.com/D60251415

Author: kazutakahirata

llvm/include/llvm/ADT/SetOperations.h

@@ -60,11 +60,11 @@ template <class S1Ty, class S2Ty> void set_intersect(S1Ty &S1, const S2Ty &S2) {
   if constexpr (detail::HasMemberRemoveIf<S1Ty, decltype(Pred)>) {
     S1.remove_if(Pred);
   } else {
-    for (typename S1Ty::iterator I = S1.begin(); I != S1.end();) {
-      const auto &E = *I;
-      ++I;
-      if (!S2.count(E))
-        S1.erase(E); // Erase element if not in S2
+    typename S1Ty::iterator Next;
+    for (typename S1Ty::iterator I = S1.begin(); I != S1.end(); I = Next) {
+      Next = std::next(I);
+      if (!S2.count(*I))
+        S1.erase(I); // Erase element if not in S2
     }
   }
 }