src/dlmisc.c:snd_dlpath_unlock() doesn't build if DL_ORIGIN_AVAILABLE is not defined

[GitHub issues - opened <github@xxxxxxxxxxxxxxxx>]

alsa-project/alsa-lib issue #91 was opened from ollieparanoid:

Hey all, thanks for maintaining alsa.

In musl libc based Alpine Linux, the build of v1.2.4 fails with:
```
dlmisc.c:95:7: error: 'snd_plugin_dir_set' undeclared (first use in this function)
   95 |  if (!snd_plugin_dir_set) {
      |       ^~~~~~~~~~~~~~~~~~
dlmisc.c:95:7: note: each undeclared identifier is reported only once for each function it appears in
dlmisc.c:98:4: error: 'snd_plugin_dir' undeclared (first use in this function)
   98 |    snd_plugin_dir = strdup(env);
      |
```

This is a regression from https://github.com/alsa-project/alsa-lib/commit/8580c081c25678d11278efcb61bd15cf44d0a225, where the #ifdef...#else...#endif was removed.

Issue URL     : https://github.com/alsa-project/alsa-lib/issues/91
Repository URL: https://github.com/alsa-project/alsa-lib