POSIX specifies that inet_ntoa() is declared in arpa/inet.h, and that
POLLRDNORM, etc. are defined in poll.h.
gethostbyname() is not specified by POSIX, but the manpages in OpenBSD,
FreeBSD, OS X, and glibc all state that it is declared in netdb.h.
Without these headers, the build fails on OpenBSD and possibly other
systems.
Most modern Unix environments use 64-bit off_t by default: OpenBSD,
FreeBSD, OS X, and Linux libc implementations such as Musl.
glibc is the lone exception; it can default to 32 bits but this is
configurable by setting _FILE_OFFSET_BITS.
Avoiding the stat64()/fstat64() interfaces is desirable because they
are nonstandard and not implemented on many systems (including
OpenBSD and FreeBSD), and using 64 bits for stat()/fstat() is either
the default or trivial to set up.
Anthony J. Bentley