These statements belong to Openldap v1.2.1:

Threads don't work with AIX (tested with 4.1.5, 4.3.x and
xlC compiler.

AIX' native NDBM is not supported. I used gdbm 1.7.3.

Additions to source code necessary because fd_set is defined in sys/select.h

add
#include <sys/select.h>
to the following files

libraries/libldap/os-ip.c
clients/finger/main.c
clients/gopher/go500gw.c
clients/gopher/go500.c
servers/slapd/daemon.c

It's possible that I forgot some files, I didn't build everything.

Developers: Please make it an #ifdef AIX in the next release :-)