[Reproducers] Include lldb version in the reproducer root

Generally, reproducers are rev-locked to the version of LLDB, so it's
valuable to have the LLDB version in the reproducer. For now I just want
the information to be present, without enforcing it, but I envision
emitting a warning during replay in the future.

Differential revision: https://reviews.llvm.org/D63229

llvm-svn: 363225