Introduce line editor library.
This library will be used by clang-query. I can imagine LLDB becoming another
client of this library, so I think LLVM is a sensible place for it to live.
It wraps libedit, and adds tab completion support.
The code is loosely based on the line editor bits in LLDB, with a few
- Polymorphism for retrieving the list of tab completions, based on the concept pattern from the new pass manager.
- Tab completion doesn't corrupt terminal output if the input covers multiple lines. Unfortunately this can only be done in a truly horrible way, as far as I can tell. But since the alternative is to implement our own line editor (which I don't think LLVM should be in the business of doing, at least for now) I think it may be acceptable.
- Includes a fallback for the case where the user doesn't have libedit installed.
Note that this uses C stdio, mainly because libedit also uses C stdio.
Differential Revision: http://llvm-reviews.chandlerc.com/D2200