vpool.h is referring cdefs.h which is not available in musl-libc
There is an error compiling knot-dns on a linux with musl-libc:
CC libknot/yparser/la-yptrafo.lo CC libdnssec/contrib/la-vpool.lo In file included from libdnssec/contrib/vpool.c:25:0: ./libdnssec/contrib/vpool.h:24:10: fatal error: sys/cdefs.h: No such file or directory #include <sys/cdefs.h>
The solution provided here: https://wiki.musl-libc.org/faq.html#Q:-When-compiling-something-against-musl,-I-get-error-messages-about-<code>sys/cdefs.h</code>