[ORC][MachO] For convenience, make MachOPlatform ref available to subclasses.

This saves SimpleMachOHeaderMU subclasses from having to hold their own
reference.

Author: lhames

llvm/include/llvm/ExecutionEngine/Orc/MachOPlatform.h

@@ -345,6 +345,8 @@ class SimpleMachOHeaderMU : public MaterializationUnit {
   virtual jitlink::Block &createHeaderBlock(JITDylib &JD, jitlink::LinkGraph &G,
                                             jitlink::Section &HeaderSection);
 
+  MachOPlatform &MOP;
+
 private:
   struct HeaderSymbol {
     const char *Name;
@@ -359,8 +361,6 @@ class SimpleMachOHeaderMU : public MaterializationUnit {
   static MaterializationUnit::Interface
   createHeaderInterface(MachOPlatform &MOP,
                         const SymbolStringPtr &HeaderStartSymbol);
-
-  MachOPlatform &MOP;
 };
 
 /// Simple MachO header graph builder.