Got this warning after running make autoconf ;
./configure (GNU Autoconf) 2.59

configure: WARNING: sys/un.h: present but cannot be
compiled
configure: WARNING: sys/un.h:     check for missing
prerequisite headers?
configure: WARNING: sys/un.h: see the Autoconf
documentation
configure: WARNING: sys/un.h:     section "Present But
Cannot Be Compiled"
configure: WARNING: sys/un.h: proceeding with the
preprocessor's result
configure: WARNING: sys/un.h: in the future, the
compiler will take precedence
configure: WARNING:     ##
--------------------------------- ##
configure: WARNING:     ## Report this to the python
lists.  ##
configure: WARNING:     ##
--------------------------------- ##