Update lldb to trunk r290819 and resolve conflicts.

Update lldb to release_39 branch r276489 and resolve immediate conflicts.

Update LLDB snapshot to upstream r216948 (git 50f7fe44)

This is approximately "LLDB 3.5" although with a little bit of skew,
and will go along with the Clang 3.5 import.

Sponsored by: DARPA, AFRL