lldb-preview "missing" in recent nightlies

[dvdplm]

There seems to be an issue with the nightly build since Nov 26. Not sure if this is a known issue or not.

[tromey]

Thanks for the report! I appreciate it because, although I did notice that lldb was disabled this time, I imagine there will be other times where I miss it. See rust-lang/rust#56298. I'm closing this as it is in progress already.