>         <arpa/inet.h> is missing a prototype for the inet_aton() function

No, it is not. It has been in there for almost a month.

revision 1.3
date: 1994/04/07 06:59:02;  author: deraadt;  state: Exp;  lines: +8 -7
new resolver. changes from 4.9.2 by <paul@vix.com>, as well as a number
of features and optimizations by myself.

Sounds like you didn't do a make install in /usr/include somewhere
along the line.

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