Build of alsa-utils 1.2.9 fails when building is a subdir

alsa-project/alsa-utils issue #212 was opened from heitbaum:

Compile errors when building in a subdir: ``` alsactl/alsactl.c:33:10: fatal error: os_compat.h: No such file or directory 33 | #include "os_compat.h" | ^~~~~~~~~~~~~ alsactl/lock.c:34:10: fatal error: os_compat.h: No such file or directory 34 | #include "os_compat.h" | ^~~~~~~~~~~~~ ```

Issue URL : https://github.com/alsa-project/alsa-utils/issues/212 Repository URL: https://github.com/alsa-project/alsa-utils