os: filesystem level locking api (#11191)

vlib/os/filelock/lib.v

@@ -0,0 +1,14 @@
+module filelock
+
+pub struct FileLock {
+	name string
+mut:
+	fd int
+}
+
+pub fn new(fileName string) FileLock {
+	return FileLock{
+		name: fileName
+		fd: -1
+	}
+}