lldb/API/LLDB.h: No such file or directory

I'm building jucipp master branch (pulled yesterday, commit 59ce9693 ) on my machine. CMake succeeds (except that plantuml isn't found), and the build proceeds, then at some point I get:

[ 34%] Building CXX object src/CMakeFiles/juci_shared.dir/source_clang.cc.o
In file included from /usr/local/src/jucipp/src/source_clang.cc:6:0:
/usr/local/src/jucipp/src/debug_lldb.h:4:27: fatal error: lldb/API/LLDB.h: No such file or directory
 #include <lldb/API/LLDB.h>
                           ^
compilation terminated.

and, indeed, I have no file named LLDB.h on my system. But then, why did CMake not indicate something is missing?

My system is Devuan ASCII, which is the same as Debian Stretch but without systemd.

(PS - I also tried downloading the release tarball, but that didn't have the submodules.)