Add Rust support to lldb

[steveklabnik]

By @brson: rust-lang/rust#19532

Calling functions in lldb among other things requires direct debugger support. We'll have to start modifying lldb.

[tromey]

I've started working on this.

[tromey]

My lldb branch is here: https://github.com/tromey/lldb/tree/rust

[tromey]

I've discussed getting this into rustup with @Mark-Simulacrum and @nrc recently. The working plan discussed today is to rebase the lldb work so it is compatible with the version of llvm in rust-llvm, then make it build as part of the llvm build step; and also at some point moving the lldb repository into the rust lang nursery.

[tromey]

I think this is needed first: rust-lang/rust-installer#85

[tromey]

rust-lang/rust#52716

[tromey]

lldb is in the rust build now. The remaining work, if any, is being done in rust-lang/rust#48168

[Centril]

Alright; since this is being tracked elsewhere I'm closing this; Thanks @tromey! :)