Esteemed maintainers (and contributors),

Attached is a patch which, as far as I can see, should work. But it does not. I would like to submit it here for review. Please tell me what I am doing wrong or what I am failing to do, so that I might clean up this patch and submit a proper one.

1. The problem this patch is trying to solve:

Aegisub (guix install aegisub), as it currently is, does not give any sound (at least on foreign distros). The terminal output reads as follows, when a video file (with audio) is added into the program and an attempt is made at playing it: (Video is added to aegisub by using 'Video > Open Video...')

```

ALSA lib conf.c:3683:(snd_config_hooks_call) Cannot open shared library libasound_module_conf_pulse.so (/gnu/store/zcjdb23gbhl0pcnvvm8rnlprkfl43cv5-alsa-lib-1.2.2/lib/alsa-lib/libasound_module_conf_pulse.so: libasound_module_conf_pulse.so: cannot open shared object file: No such file or directory)
ALSA lib pcm.c:2642:(snd_pcm_open_noupdate) Unknown PCM default

```

The complaint being that it can't find libasound_module_conf_pulse.so. This .so comes from the guix package `alsa-plugins:pulseaudio`. The /gnu/store directory for it is something like /gnu/store/...-alsa-plugins-1.2.2-pulseaudio/lib/alsa-lib/libasound_module_conf_pulse.so. However, the .so file is being looked for inside of the /gnu/store path to alsa-lib (/gnu/store/...-alsa-lib-1.2.2/lib/alsa-lib/libasound_module_conf_pulse.so.

2. The Natural Solution:

Since libasound_module_conf_pulse.so is supplied by `alsa-plugins:pulseaudio`, and the program is looking for it inside the path to alsa-lib (supplied by `alsa-lib`), union-build is a logical solution. This is what the patch implements.

3. Problem:

Despite this patch being applied, it continues to look for the .so file inside the path to alsa-lib and not the union-alsa. What is more, alsa-lib is not even in the inputs. Only union-alsa is. And yet, it seems to be trying to use alsa-lib's /gnu/store path, which, the way I see it, violates guix's functional package management.

4. It's not guix, it's me:

I'm sure this is some mistake on my part. Hence, I submit the diff here for review.

P. S: The diff has changed a bit because I got this idea of moving out/lib/alsa-lib/* into out/lib/ just to see if that makes any difference. Only to realize a little too late that it doesn't. But I send the diff with those changes included because I didn't stash the previous (cleaner) one.