meson: Respect ldap option
Only build LDAP provider if requested.
Also fix configuration failure if openldap is not installed:
tools/meson.build:149:0: ERROR: Unknown variable "libldap_provider".
Only build LDAP provider if requested.
Also fix configuration failure if openldap is not installed:
tools/meson.build:149:0: ERROR: Unknown variable "libldap_provider".