[Stdlib] Add some prespecializations to the stdlib

This adds prespecializations for commonly used types to the stdlib

Author: drexin

lib/DriverTool/sil_opt_main.cpp

@@ -614,6 +614,8 @@ int sil_opt_main(ArrayRef<const char *> argv, void *MainAddr) {
     options.EnableObjCInterop ? true :
     options.DisableObjCInterop ? false : llvm::Triple(options.Target).isOSDarwin();
 
+  Invocation.getLangOptions().Features.insert(Feature::LayoutPrespecialization);
+
   Invocation.getLangOptions().OptimizationRemarkPassedPattern =
       createOptRemarkRegex(options.PassRemarksPassed);
   Invocation.getLangOptions().OptimizationRemarkMissedPattern =

lib/Frontend/CompilerInvocation.cpp

@@ -838,6 +838,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   if (Args.hasArg(OPT_enable_builtin_module))
     Opts.Features.insert(Feature::BuiltinModule);
 
+  Opts.Features.insert(Feature::LayoutPrespecialization);
+
   Opts.EnableAppExtensionRestrictions |= Args.hasArg(OPT_enable_app_extension);
 
   Opts.EnableSwift3ObjCInference =