[SSSD] [PATCH] Fix two problems with --as-needed

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Hi, On Fedora, I saw two problems when building and using sssd with - -Wl,--as-needed:

The configure-time check for HAVE_DBUS_WATCH_GET_UNIX_FD wasn't run correctly which resulted in using the deprecated DBus function and subsequent GCC warning. The other issue was that the LDAP backend wouldn't start and complained about "libsss_ldap.so: undefined symbol: hash_error_string".

The attached patch addresses them. It is at least partial fix for #559.

Jakub