flex: Fix --noline option behavior

Option --noline or -L does not handled properly.
So generated code contains #line directives with
file absolute path and prevents to create
reproducible builds.

Signed-off-by: Oleksiy Obitotskyy <oobitots@cisco.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 0bf2cb7d)
Signed-off-by: Steve Sakoman <steve@sakoman.com>