Add BuiltinCreateTaskGroupWithFlags feature and use it to guard the builtin

Author: DougGregor

include/swift/Basic/Features.def

@@ -86,6 +86,7 @@ LANGUAGE_FEATURE(BuiltinTaskRunInline, 0, "Builtin.taskRunInline", true)
 LANGUAGE_FEATURE(BuiltinUnprotectedAddressOf, 0, "Builtin.unprotectedAddressOf", true)
 SUPPRESSIBLE_LANGUAGE_FEATURE(SpecializeAttributeWithAvailability, 0, "@_specialize attribute with availability", true)
 LANGUAGE_FEATURE(BuiltinAssumeAlignment, 0, "Builtin.assumeAlignment", true)
+LANGUAGE_FEATURE(BuiltinCreateTaskGroupWithFlags, 0, "Builtin.createTaskGroupWithFlags", true)
 SUPPRESSIBLE_LANGUAGE_FEATURE(UnsafeInheritExecutor, 0, "@_unsafeInheritExecutor", true)
 SUPPRESSIBLE_LANGUAGE_FEATURE(PrimaryAssociatedTypes2, 346, "Primary associated types", true)
 SUPPRESSIBLE_LANGUAGE_FEATURE(UnavailableFromAsync, 0, "@_unavailableFromAsync", true)

lib/AST/ASTPrinter.cpp

@@ -2938,6 +2938,10 @@ static bool usesFeatureBuiltinTaskRunInline(Decl *) { return false; }
 
 static bool usesFeatureBuiltinUnprotectedAddressOf(Decl *) { return false; }
 
+static bool usesFeatureBuiltinCreateTaskGroupWithFlags(Decl *decl) {
+  return false;
+}
+
 static bool usesFeatureSpecializeAttributeWithAvailability(Decl *decl) {
   if (auto func = dyn_cast<AbstractFunctionDecl>(decl)) {
     for (auto specialize : func->getAttrs().getAttributes<SpecializeAttr>()) {

stdlib/public/Concurrency/DiscardingTaskGroup.swift

@@ -74,7 +74,7 @@ public func withDiscardingTaskGroup<GroupResult>(
   returning returnType: GroupResult.Type = GroupResult.self,
   body: (inout DiscardingTaskGroup) async -> GroupResult
 ) async -> GroupResult {
-  #if compiler(>=5.5) && $BuiltinTaskGroupWithArgument
+  #if compiler(>=5.5) && $BuiltinCreateTaskGroupWithFlags
   let flags = taskGroupCreateFlags(
     discardResults: true
   )
@@ -378,7 +378,7 @@ public func withThrowingDiscardingTaskGroup<GroupResult>(
     returning returnType: GroupResult.Type = GroupResult.self,
     body: (inout ThrowingDiscardingTaskGroup<Error>) async throws -> GroupResult
 ) async throws -> GroupResult {
-  #if compiler(>=5.5) && $BuiltinTaskGroupWithArgument
+  #if compiler(>=5.5) && $BuiltinCreateTaskGroupWithFlags
   let flags = taskGroupCreateFlags(
       discardResults: true
   )