[clang-repl] Add an accessor to our underlying execution engine

This patch will allow better incremental adoption of these changes in downstream
cling and other users which want to experiment by customizing the execution
engine.

(cherry picked from commit 788e0f7)

Author: vgvassilev

clang/include/clang/Interpreter/Interpreter.h

@@ -26,6 +26,7 @@
 
 namespace llvm {
 namespace orc {
+class LLJIT;
 class ThreadSafeContext;
 }
 } // namespace llvm
@@ -56,6 +57,7 @@ class Interpreter {
   static llvm::Expected<std::unique_ptr<Interpreter>>
   create(std::unique_ptr<CompilerInstance> CI);
   const CompilerInstance *getCompilerInstance() const;
+  const llvm::orc::LLJIT *getExecutionEngine() const;
   llvm::Expected<PartialTranslationUnit &> Parse(llvm::StringRef Code);
   llvm::Error Execute(PartialTranslationUnit &T);
   llvm::Error ParseAndExecute(llvm::StringRef Code) {

clang/lib/Interpreter/IncrementalExecutor.h

@@ -45,6 +45,7 @@ class IncrementalExecutor {
   llvm::Error runCtors() const;
   llvm::Expected<llvm::JITTargetAddress>
   getSymbolAddress(llvm::StringRef Name, SymbolNameKind NameKind) const;
+  llvm::orc::LLJIT *getExecutionEngine() const { return Jit.get(); }
 };
 
 } // end namespace clang

clang/lib/Interpreter/Interpreter.cpp

@@ -196,6 +196,12 @@ const CompilerInstance *Interpreter::getCompilerInstance() const {
   return IncrParser->getCI();
 }
 
+const llvm::orc::LLJIT *Interpreter::getExecutionEngine() const {
+  if (IncrExecutor)
+    return IncrExecutor->getExecutionEngine();
+  return nullptr;
+}
+
 llvm::Expected<PartialTranslationUnit &>
 Interpreter::Parse(llvm::StringRef Code) {
   return IncrParser->Parse(Code);