ClangFunction: Fix destruction order of parser and execution unit

Fix PR21802 by correcting the destruction order of
`ClangExpressionParser` and `IRExecutionUnit` in `ClangFunction`.  The
former has hooks into the latter -- i.e., `clang::CGDebugInfo` points at
the `LLVMContext` -- so it needs to be torn down first.

This was exposed by r223802 in LLVM, which started doing work in the
`CGDebugInfo` teardown.

llvm-svn: 223916

lldb/include/lldb/Expression/ClangFunction.h

@@ -411,8 +411,10 @@ private:
     // For ClangFunction only
     //------------------------------------------------------------------
 
-    std::unique_ptr<ClangExpressionParser> m_parser;                 ///< The parser responsible for compiling the function.
+    // Note: the parser needs to be destructed before the execution unit, so
+    // declare the the execution unit first.
     std::shared_ptr<IRExecutionUnit> m_execution_unit_sp;
+    std::unique_ptr<ClangExpressionParser> m_parser;                 ///< The parser responsible for compiling the function.
     lldb::ModuleWP                  m_jit_module_wp;
     std::string                     m_name;                         ///< The name of this clang function - for debugging purposes.
     

lldb/source/Expression/ClangFunction.cpp

@@ -57,8 +57,8 @@ ClangFunction::ClangFunction
     const ValueList &arg_value_list,
     const char *name
 ) :
-    m_parser(),
     m_execution_unit_sp(),
+    m_parser(),
     m_jit_module_wp(),
     m_name (name ? name : "<unknown>"),
     m_function_ptr (NULL),