Fix bug #28898

lldb: libedit produces garbled, unusable input on Linux

Apply patch from Christos Zoulas, upstream libedit developer.
It has been tested on NetBSD/amd64.

New code supports combination of wide libedit and disabled
LLDB_EDITLINE_USE_WCHAR, which was the popular case on Linux
systems.

llvm-svn: 303907