I managed to build LLDB on a Beaglebone Black running a snapshot (May 20th) of FreeBSD 12.0-CURRENT -- ARMv6. This is the first LLDB of all that I tried out, which let me single step into the code, so I am already quite happy with it. In the moment, I see only one minor issue left to be resolved, namely UTF8 strings are not displayed correctly in the ncurses-GUI mode, while in cli mode I see no issue.
This happens in the ncurses-GUI mode of LLDB 3.9.1, LLDB 4.0.1, up to LLDB 5.0.0 (svn).
This is an ARM issue, since it does not occur on x86 machines. Perhaps this might be related to the signed/unsigned char mismatch between ARM and x86. Other ncurses software on the Beaglebone does work well under FreeBSD.
I did not find a bug-reporting facility for LLDB. In case, I need to submit a bug report on this, please may I ask for a link.