Add support for musl-libc (endian.h)
Add support for musl-libc (endian.h)

musl supports the soon-to-be standardized endian.h, while FreeBSD only
supports sys/endian.h as of now, so check for FreeBSD here, as other
operating systems will likely support endian.h in the future.

Signed-off-by: Christian Seiler <2314b2e3a4a1f7db165be2aafbf1efd78f28cc97@iwakd.de>

gonzoleeman/open-isns,gonzoleeman/open-isns,gonzoleeman/open-isns