Revert "Drop the -ubuntu-18.04.tar.xz builds"

This reverts commit b1640280a5.

Turns out these builds do work fine, I just forgot to disable unity
builds for them.

CHANGELOG.md

@@ -19,11 +19,6 @@ Versioning](https://semver.org/spec/v2.0.0.html).
   with yabridge, then do consider
   [downgrading](https://github.com/robbert-vdh/yabridge#downgrading-wine) back
   to Wine Staging 7.20.
-
-  **The `-ubuntu-18.04.tar.xz` builds are no longer provided from this release
-  as they were still affected by the abovementioned bug despite all of the
-  workarounds.**
-
 - Yabridge's build system now errors out when enabling unity builds while
   compiling with Wine 7.21 and 7.22.
 

README.md

@@ -104,7 +104,10 @@ Please let me know if there are any issues with other hosts.
      distro, you can simply download and install a prebuilt version of yabridge:
 
      1. First download the latest version of yabridge from the [releases
-        page](https://github.com/robbert-vdh/yabridge/releases).
+        page](https://github.com/robbert-vdh/yabridge/releases). If you're using
+        a distro that's older than Ubuntu 20.04 such as Ubuntu 18.04, Debian 10,
+        Linux Mint 19, or AV Linux MXE 2021, then you should download the
+        version that ends with `-ubuntu-18.04.tar.gz`.
      2. Extract the contents of the downloaded archive to `~/.local/share`, such
         that the file `~/.local/share/yabridge/yabridgectl` exists after
         extracting. You can extract an archive here from the command line with