dns/bind9-devel: Set LDFLAGS for ports-based libedit/ncurses
The latest version failed to configure using ports libedit+ncurses:
configure: checking for readline with -ledit checking for readline... no configure: checking for readline with -ledit -lterminfo checking for readline... no configure: checking for readline with -ledit -ltermcap checking for readline... no configure: checking for readline with -ledit -lncurses checking for readline... no configure: checking for readline with -ledit -lcurses checking for readline... no configure: error: The readline library was not found.
Setting LDFLAGS allows the build to complete as before.
Approved by: just-fix-it/explicit LDFLAGS blanket