[Frontend] Output the private module interface with the SPI info

include/swift/Frontend/ModuleInterfaceSupport.h

@@ -39,6 +39,9 @@ struct ModuleInterfaceOptions {
   /// generation time, re-applied to CompilerInvocation when reading
   /// back .swiftinterface and reconstructing .swiftmodule.
   std::string Flags;
+
+  // Print SPI decls and attributes.
+  bool PrintSPIs = false;
 };
 
 extern version::Version InterfaceFormatVersion;
@@ -50,7 +53,7 @@ llvm::Regex getSwiftInterfaceModuleFlagsRegex();
 /// source file to import this module, subject to options given by \p Opts.
 ///
 /// Unlike a serialized module, the textual format generated by
-/// emitModuleInterface is intended to be stable across compiler versions while
+/// emitSwiftInterface is intended to be stable across compiler versions while
 /// still describing the full ABI of the module in question.
 ///
 /// The initial plan for this format can be found at