BUG #16042: incorrect .gitignore file

The following bug has been logged on the website:

Bug reference:      16042
Logged by:          Denis Stuchalin
Email address:      stuchalin.d@gmail.com
PostgreSQL version: 11.5
Operating system:   Linux
Description:

The sourses repository https://www.postgresql.org/ftp/source/v11.5/.
The source codes contain the file src/bin/pg_waldump/.gitignore
This file contains the line /*desc.c
This line does not give the correct commit file rmgrdesc.c from this
directory to the "my" git repository.
This problem does not allow to build a postgresql cloned from "my" git
repository, since git does not have the file need to build successfully.

Workflow:
1. Download souses from https://www.postgresql.org/ftp/source/v11.5/
2. Push sourses into GIT repo
3. Clone souses from GIT into other place.
4. Build from cloned sourses FAILED.