Share my binary package:
http://rockpro64.ddns.net/seafile-server_6.3.4_arm64.tar.gz
(for Ubuntu 18.04LTS only, gcc7 compiler, GLIBC_VER2.5)
install ldap development package :
sudo apt install libldap2-dev
my build includes ldap feature
http://rockpro64.ddns.net/seafile-server_6.3.4_arm64_gcc6.tar.gz
(for Ubuntu 16.04LTS )