soelim, a part of groff, is required to build openldap.

component/groff/buildout.cfg

+[buildout]
+parts =
+  groff
+
+[groff]
+recipe = hexagonit.recipe.cmmi
+url = http://ftp.gnu.org/gnu/groff/groff-1.21.tar.gz
+md5sum = 8b8cd29385b97616a0f0d96d0951c5bf
+configure-options =
+  --disable-static
+  --without-x

component/openldap/buildout.cfg

@@ -2,6 +2,7 @@
 parts =
   openldap
 extends =
+  ../groff/buildout.cfg
   ../openssl/buildout.cfg
   ../cyrus-sasl/buildout.cfg
 
@@ -24,3 +25,4 @@ configure-options =
 environment =
   CPPFLAGS=-I${openssl:location}/include -I${cyrus-sasl:location}/include
   LDFLAGS=-L${openssl:location}/lib -Wl,-rpath=${openssl:location}/lib -L${cyrus-sasl:location}/lib -Wl,-rpath=${cyrus-sasl:location}/lib
+  PATH=${groff:location}/bin:%(PATH)s