Systemd commit [bf1b9ae487b65b1cb1639b222724fab95e508cf5](bf1b9ae487) (present in Systemd v254 and later) effectively broke gamemodelist as the process map for the `systemd --user` process became unreadable. After this change gamemodelist would exit with an error like the following:
```
awk: fatal: cannot open file `/proc/2281/maps' for reading: Permission denied
```
To work around this let's add a hook to the awk statement to skip any files that can't be read.
ClosesFeralInteractive/gamemode#456
* New utility: gamemodelist
While trying out gamemode on Ubuntu 18.04 I had trouble figuring out
whether or not my games were running with gamemode enabled. I wrote this
utility which prints all processes loaded with the gamemode shared
library.
- [x] Added utility to `data/` folder.
- [x] Update meson installer.
- [x] Included section 1 manual.
- [x] Updated README for Ubuntu 18.04 build instructions. Steam supports
Ubuntu 18.04.
I'm open to feedback and generally this should work for any distrobution
since it makes use of the Linux `/proc` filesystem. [Learn more about
`/proc`][1].
[1]: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/Documentation/filesystems/proc.rst?h=v5.15.12
