CMake: fix search of LAME from system with module from Mixxx

[Be-ing]

Mixxx is licensed GPLv2 or later. This CMake module comes from:
https://github.com/mixxxdj/mixxx/blob/main/cmake/modules/Findmp3lame.cmake
Thanks to @Holzhaus for writing the CMake module.

Signed-off-by: Be be@mixxx.org

Resolves: #225

I am not certain if this fully works yet because there are still other build problems using system libraries.

• I have signed off my commits using -s or Signed-off-by* (See: Contributing § DCO)
• I made sure the code compiles on my machine
• I made sure there are no unnecessary changes in the code*
• I made sure the title of the PR reflects the core meaning of the issue you are solving*
• I made sure the commit message(s) contain a description and answer the question "Why do those changes fix that particular issue?" or "Why are those changes really necessary as improvements?"*

* indicates required

[Be-ing]

Audacity can't copy this fix because it is licensed GPL v2 or later 😁

[fossdd]

Can you add lame to the .builds/archlinux.yml file, to fix the builds.sr.ht CI?

[nbsp]

Can you add lame to the .builds/archlinux.yml file, to fix the builds.sr.ht CI?

There's an almost-comprehensive list of the packages for building without conan somewhere here, in a failed Archlinux build.

[Be-ing]

Closing in favor of #228