[cling] Use single Parser for LookupHelper

It is the only construction of a temporary parser, and it seems not
necessary (anymore).

interpreter/cling/include/cling/Interpreter/LookupHelper.h

@@ -56,7 +56,7 @@ namespace cling {
       WithDiagnostics
     };
   private:
-    std::unique_ptr<clang::Parser> m_Parser;
+    clang::Parser* m_Parser;
     Interpreter* m_Interpreter; // we do not own.
     std::array<const clang::Type*, kNumCachedStrings> m_StringTy = {{}};
     /// A map containing the hash of the lookup buffer. This allows us to avoid

interpreter/cling/lib/Interpreter/Interpreter.cpp

@@ -265,13 +265,6 @@ namespace cling {
     }
 
     Sema& SemaRef = getSema();
-    Preprocessor& PP = SemaRef.getPreprocessor();
-
-    m_LookupHelper.reset(new LookupHelper(new Parser(PP, SemaRef,
-                                                     /*SkipFunctionBodies*/false,
-                                                     /*isTemp*/true), this));
-    if (!m_LookupHelper)
-      return;
 
     if (!isInSyntaxOnlyMode() && !m_Opts.CompilerOpts.CUDADevice) {
       m_Executor.reset(new IncrementalExecutor(SemaRef.Diags, *getCI(),
@@ -317,6 +310,10 @@ namespace cling {
       return;
     }
 
+    m_LookupHelper.reset(new LookupHelper(m_IncrParser->getParser(), this));
+    if (!m_LookupHelper)
+      return;
+
     // When not using C++ modules, we now have a PCH and we can safely setup
     // our callbacks without fearing that they get overwritten by clang code.
     // The modules setup is handled above.