Skip building directio on platforms that don't support Direct IO (#9059)

pkg/disk/directio_unix.go

@@ -1,7 +1,7 @@
 // +build linux netbsd freebsd
 
 /*
- * Minio Cloud Storage, (C) 2019 Minio, Inc.
+ * Minio Cloud Storage, (C) 2019-2020 Minio, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -42,3 +42,8 @@ func DisableDirectIO(f *os.File) error {
 	_, err = unix.FcntlInt(fd, unix.F_SETFL, flag)
 	return err
 }
+
+// AlignedBlock - pass through to directio implementation.
+func AlignedBlock(BlockSize int) []byte {
+	return directio.AlignedBlock(BlockSize)
+}