SILOptimizer: add a mechanism to pre-specialize internal stdlib symbols for OnoneSupport.

When compiling the OnoneSupport library, the compiler checks for @_semantics("prespecialize.X") attributes to pre-specialize function X.

rdar://problem/48924409

include/swift/SIL/SILModule.h

@@ -266,16 +266,16 @@ private:
   SILModule(const SILModule&) = delete;
   void operator=(const SILModule&) = delete;
 
-  /// Method which returns the SerializedSILLoader, creating the loader if it
-  /// has not been created yet.
-  SerializedSILLoader *getSILLoader();
-
   /// Folding set for key path patterns.
   llvm::FoldingSet<KeyPathPattern> KeyPathPatterns;
 
 public:
   ~SILModule();
 
+  /// Method which returns the SerializedSILLoader, creating the loader if it
+  /// has not been created yet.
+  SerializedSILLoader *getSILLoader();
+
   /// Add a callback for each newly deserialized SIL function body.
   void registerDeserializationNotificationHandler(
       std::unique_ptr<DeserializationNotificationHandler> &&handler);