* src/control/control.c patch uses ALSA_PLUGIN_DIR and then, if necessary,
GUIX_ALSA_PLUGIN_DIRS.  But src/dlmisc.c uses only GUIX_ALSA_PLUGIN_DIRS,
no ALSA_PLUGIN_DIR. src/pcm/pcm.c uses ALSA_PLUGIN_DIR and then, if necessary,
GUIX_ALSA_PLUGIN_DIRS.  Is that discrepancy on purpose?