syscall: handle errors.ErrUnsupported in isNotSupported

Updates #41198

Change-Id: Ifed913f6088b77abc7a21d2a79168a20799f9d0e
Reviewed-on: https://go-review.googlesource.com/c/go/+/475857
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>

src/syscall/exec_linux_test.go

@@ -39,6 +39,8 @@ func isNotSupported(err error) bool {
 		switch errno {
 		case syscall.ENOSYS, syscall.ENOTSUP:
 			// Explicitly not supported.
+			// TODO(#41198): remove these cases when errors.Is reports that they are
+			// equivalent to ErrUnsupported.
 			return true
 		case syscall.EPERM, syscall.EROFS:
 			// User lacks permission: either the call requires root permission and the
@@ -51,12 +53,10 @@ func isNotSupported(err error) bool {
 		}
 	}
 
-	if errors.Is(err, fs.ErrPermission) {
+	if errors.Is(err, fs.ErrPermission) || errors.Is(err, errors.ErrUnsupported) {
 		return true
 	}
 
-	// TODO(#41198): Also return true if errors.Is(err, errors.ErrUnsupported).
-
 	return false
 }