[cling] Clear JITDylibs manually to avoid assertion failure

We started seeing an assertion failure in ~FinalizedAlloc after
commit 4565a9d. Likely changed the destruction order that caused
the assertion to trigger.

Author: devajithvs

interpreter/cling/lib/Interpreter/IncrementalJIT.cpp

@@ -438,6 +438,17 @@ namespace cling {
 ///\brief Creates JIT event listener to allow profiling of JITted code with perf
 llvm::JITEventListener* createPerfJITEventListener();
 
+IncrementalJIT::~IncrementalJIT() {
+  // FIXME: This should ideally happen in the right order without explicitly
+  // doing this. We started seeing failing tests (eg, tutorial-hist-cumulative,
+  // JITLink turned on) with assertion failure in ~FinalizedAlloc after commit
+  // 4565a9d5d1 [cling] Move generators to ProcessSymbols JITDylib
+  // This likely changed the destruction order that caused the assertion to
+  // trigger.
+  Jit->getMainJITDylib().clear();
+  Jit->getProcessSymbolsJITDylib()->clear();
+}
+
 IncrementalJIT::IncrementalJIT(
     IncrementalExecutor& Executor, const clang::CompilerInstance &CI,
     std::unique_ptr<llvm::orc::ExecutorProcessControl> EPC, Error& Err,

interpreter/cling/lib/Interpreter/IncrementalJIT.h

@@ -62,6 +62,8 @@ class IncrementalJIT {
                  std::unique_ptr<llvm::orc::ExecutorProcessControl> EPC,
                  llvm::Error &Err, void *ExtraLibHandle, bool Verbose);
 
+  ~IncrementalJIT();
+
   /// Register a DefinitionGenerator to dynamically provide symbols for
   /// generated code that are not already available within the process.
   void addGenerator(std::unique_ptr<llvm::orc::DefinitionGenerator> G) {