[clang-repl] Fix remove invalidates iterators in CleanUpPTU() (#85378)

Using remove() on DeclContext::lookup_result list invalidates iterators.

This assertion failure was one (fortunate) symptom:
```
clang/include/clang/AST/DeclBase.h:1337: reference clang::DeclListNode::iterator::operator*() const: Assertion `Ptr && "dereferencing end() iterator"' failed.
```

Author: weliveindetail

clang/include/clang/AST/DeclContextInternals.h

@@ -205,7 +205,7 @@ class StoredDeclsList {
     Data.setPointer(Head);
   }
 
-  /// Return an array of all the decls that this list represents.
+  /// Return the list of all the decls.
   DeclContext::lookup_result getLookupResult() const {
     return DeclContext::lookup_result(Data.getPointer());
   }

clang/lib/Interpreter/IncrementalParser.cpp

@@ -375,16 +375,22 @@ void IncrementalParser::CleanUpPTU(PartialTranslationUnit &PTU) {
   TranslationUnitDecl *MostRecentTU = PTU.TUPart;
   TranslationUnitDecl *FirstTU = MostRecentTU->getFirstDecl();
   if (StoredDeclsMap *Map = FirstTU->getPrimaryContext()->getLookupPtr()) {
-    for (auto I = Map->begin(); I != Map->end(); ++I) {
-      StoredDeclsList &List = I->second;
+    for (auto &&[Key, List] : *Map) {
       DeclContextLookupResult R = List.getLookupResult();
+      std::vector<NamedDecl *> NamedDeclsToRemove;
+      bool RemoveAll = true;
       for (NamedDecl *D : R) {
-        if (D->getTranslationUnitDecl() == MostRecentTU) {
+        if (D->getTranslationUnitDecl() == MostRecentTU)
+          NamedDeclsToRemove.push_back(D);
+        else
+          RemoveAll = false;
+      }
+      if (LLVM_LIKELY(RemoveAll)) {
+        Map->erase(Key);
+      } else {
+        for (NamedDecl *D : NamedDeclsToRemove)
           List.remove(D);
-        }
       }
-      if (List.isNull())
-        Map->erase(I);
     }
   }
 }