I did this

CPPFLAGS="-I/opt/include" CFLAGS="-I/opt/include -O2 -qmaxmem=-1 -qarch=pwr5"
../src/curl-7.64.0/configure
--prefix=/opt
--sysconfdir=/var/curl/etc
--sharedstatedir=/var/curl/com
--localstatedir=/var/curl
--mandir=/usr/share/man
--infodir=/opt/share/info/curl --with-ca-bundle=/var/ssl/cacert.pem --with-libssh2=/opt --with-zlib=/opt --enable-ldap --enable-ldaps --with-ldap=/opt

I did not expect

configure: WARNING: Cannot find libraries for LDAP support: LDAP disabled

operating system

AIX 5.3, AIX 6.1 and AIX 7.1