MFC r359453, r359455

r359453:
flua: enable readline bits, courtesy of libedit

This is a nicer experience when attempting to run ad-hoc lua bits in the
flua REPL.

r359455:
flua: follow-up to r359453, don't bother with libedit in bootstrap

The bootstrap flua should not be used for REPL-like activities; exclude it
to save the dependency on libedit and not waste time with it.

PR: 245121