util.h: endian.h is available on musl on linux

[kraj]

just checking for glibc alone is not enough since it excludes musl, therefore check for platform being linux as well

Fixes build issues

include/libisns/util.h:114:12: fatal error: sys/endian.h: No such file or directory

include <sys/endian.h>

        ^~~~~~~~~~~~~~

Signed-off-by: Khem Raj raj.khem@gmail.com

[gonzoleeman]

Looks good to me. Thank you.