I was able to build it with openssl instead.
 

Yes, it did.

/bin/sh ../../libtool  --mode=compile cc -g -O2 -I../../include        -I../../include   -I/usr/include -I/usr/include/nss -I/usr/include/nspr -I/usr/local/ssl/include   -DLDAP_LIBRARY -c tls_m.c
 cc -g -O2 -I../../include -I../../include -I/usr/include -I/usr/include/nss -I/usr/include/nspr -I/usr/local/ssl/include -DLDAP_LIBRARY -c tls_m.c  -fPIC -DPIC -o .libs/tls_m.o
 
...

/bin/sh ../../libtool  --mode=link cc -g -O2  -L/usr/lib/nss -L/usr/local/lib -L/usr/local/libexec -L/usr/lib64 -L/usr/local/ssl/lib  -release 2.4 -version-info 9:1:7 -rpath /usr/local/lib -o libldap.la bind.lo open.lo result.lo error.lo compare.lo search.lo controls.lo messages.lo references.lo extended.lo cyrus.lo modify.lo add.lo modrdn.lo delete.lo abandon.lo sasl.lo gssapi.lo sbind.lo unbind.lo cancel.lo filter.lo free.lo sort.lo passwd.lo whoami.lo getdn.lo getentry.lo getattr.lo getvalues.lo addentry.lo request.lo os-ip.lo url.lo pagectrl.lo sortctrl.lo vlvctrl.lo init.lo options.lo print.lo string.lo util-int.lo schema.lo charray.lo os-local.lo dnssrv.lo utf-8.lo utf-8-conv.lo tls2.lo tls_o.lo tls_g.lo tls_m.lo turn.lo ppolicy.lo dds.lo txn.lo ldap_sync.lo stctrl.lo assertion.lo deref.lo ldif.lo fetch.lo version.lo  ../../libraries/liblber/liblber.la -lresolv    -lssl3 -lsmime3 -lnss3 -lnssutil3 -lplds4 -lplc4 -lnspr4
cc -shared  .libs/bind.o .libs/open.o .libs/result.o .libs/error.o .libs/compare.o .libs/search.o .libs/controls.o .libs/messages.o .libs/references.o .libs/extended.o .libs/cyrus.o .libs/modify.o .libs/add.o .libs/modrdn.o .libs/delete.o .libs/abandon.o .libs/sasl.o .libs/gssapi.o .libs/sbind.o .libs/unbind.o .libs/cancel.o .libs/filter.o .libs/free.o .libs/sort.o .libs/passwd.o .libs/whoami.o .libs/getdn.o .libs/getentry.o .libs/getattr.o .libs/getvalues.o .libs/addentry.o .libs/request.o .libs/os-ip.o .libs/url.o .libs/pagectrl.o .libs/sortctrl.o .libs/vlvctrl.o .libs/init.o .libs/options.o .libs/print.o .libs/string.o .libs/util-int.o .libs/schema.o .libs/charray.o .libs/os-local.o .libs/dnssrv.o .libs/utf-8.o .libs/utf-8-conv.o .libs/tls2.o .libs/tls_o.o .libs/tls_g.o .libs/tls_m.o .libs/turn.o .libs/ppolicy.o .libs/dds.o .libs/txn.o .libs/ldap_sync.o .libs/stctrl.o .libs/assertion.o .libs/deref.o .libs/ldif.o .libs/fetch.o .libs/version.o  -Wl,--rpath -Wl,/home/wuschi/ldap/openldap-2.4.26/libraries/liblber/.libs -L/usr/lib/nss -L/usr/local/lib -L/usr/local/libexec -L/usr/lib64 -L/usr/local/ssl/lib ../../libraries/liblber/.libs/liblber.so -lresolv -lssl3 -lsmime3 -lnss3 -lnssutil3 -lplds4 -lplc4 -lnspr4  -Wl,-soname -Wl,libldap-2.4.so.2 -o .libs/libldap-2.4.so.2.7.1
(cd .libs && rm -f libldap-2.4.so.2 && ln -s libldap-2.4.so.2.7.1 libldap-2.4.so.2)
(cd .libs && rm -f libldap.so && ln -s libldap-2.4.so.2.7.1 libldap.so)
ar cru .libs/libldap.a  bind.o open.o result.o error.o compare.o search.o controls.o messages.o references.o extended.o cyrus.o modify.o add.o modrdn.o delete.o abandon.o sasl.o gssapi.o sbind.o unbind.o cancel.o filter.o free.o sort.o passwd.o whoami.o getdn.o getentry.o getattr.o getvalues.o addentry.o request.o os-ip.o url.o pagectrl.o sortctrl.o vlvctrl.o init.o options.o print.o string.o util-int.o schema.o charray.o os-local.o dnssrv.o utf-8.o utf-8-conv.o tls2.o tls_o.o tls_g.o tls_m.o turn.o ppolicy.o dds.o txn.o ldap_sync.o stctrl.o assertion.o deref.o ldif.o fetch.o version.o
ranlib .libs/libldap.a