use posix basename to fix build on musl

glibc provides a nonstandard basename implementation,
this can be overriden and posix basename can be used
by includeing libgen.h, however musl only has posix
basename, and must always include libgen.h

In this particular case, it doesn't appear that using
the posix version of basename will cause any issues,
as it is simply being used to match a hardcoded config
file name.

daemon/gamemode-config.c

@@ -41,6 +41,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include <ini.h>
 
 #include <dirent.h>
+#include <libgen.h>
 #include <math.h>
 #include <pthread.h>
 #include <pwd.h>