[clang] Delete entry in LinkModules when std::moving the inner Module

[argentite]

Summary

LinkInModules() seems to assume it will be called only once and it
std::moves the inner Module from each LinkModule without deleting the
LinkModule itself causing nullptr dereferences in subsequent calls.

clang/lib/CodeGen/CodeGenAction.cpp

void HandleInterestingDecl(DeclGroupRef D) override {
       // Ignore interesting decls from the AST reader after IRGen is finished.
       if (!IRGenFinished)
         HandleTopLevelDecl(D);
     }
 
     // Links each entry in LinkModules into our module.  Returns true on error.
     bool LinkInModules() {
       for (auto &LM : LinkModules) {
+        assert(LM.Module && "LinkModule does not actually have a module");
         if (LM.PropagateAttrs)
           for (Function &F : *LM.Module) {
             // Skip intrinsics. Keep consistent with how intrinsics are created
             // in LLVM IR.
             if (F.isIntrinsic())
               continue;
             Gen->CGM().addDefaultFunctionDefinitionAttributes(F);
           }
bool LinkInModules() {
         } else {
           Err = Linker::linkModules(*getModule(), std::move(LM.Module),
                                     LM.LinkFlags);
         }
 
         if (Err)
           return true;
       }
+      LinkModules.clear();
       return false; // success
     }
 
     void HandleTranslationUnit(ASTContext &C) override {
       {
         llvm::TimeTraceScope TimeScope("Frontend");
         PrettyStackTraceString CrashInfo("Per-file LLVM IR generation");
         if (TimerIsEnabled) {