Cmake error when trying to build on Ubuntu VM

[Chee-Tzu]

$ cmake -S . -B build -DUBPF_ENABLE_TESTS=true
cmake --build build --config Debug
-- The C compiler identification is GNU 11.4.0
-- The CXX compiler identification is GNU 11.4.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Looking for pow in m
-- Looking for pow in m - found
CMake Error at /usr/share/cmake-3.22/Modules/ExternalProject.cmake:2882 (message):
  No download info given for 'Conformance' and its source directory:

   /home/cheetzu/Documents/bi0s/ubpf/external/bpf_conformance

  is not an existing non-empty directory.  Please specify one of:

   * SOURCE_DIR with an existing non-empty directory
   * DOWNLOAD_COMMAND
   * URL
   * GIT_REPOSITORY
   * SVN_REPOSITORY
   * HG_REPOSITORY
   * CVS_REPOSITORY and CVS_MODULE
Call Stack (most recent call first):
  /usr/share/cmake-3.22/Modules/ExternalProject.cmake:3716 (_ep_add_download_command)
  CMakeLists.txt:24 (ExternalProject_Add)


CMake Warning at bpf/CMakeLists.txt:69 (message):
  Clang supports BPF target


-- Building BPF map
-- Building BPF rel_64_32
-- Configuring incomplete, errors occurred!
See also "/home/cheetzu/Documents/bi0s/ubpf/build/CMakeFiles/CMakeOutput.log".
gmake: Makefile: No such file or directory
gmake: *** No rule to make target 'Makefile'.  Stop.`

------------ Release Version -------------
$ lsb_release -a 
No LSB modules are available.
Distributor ID:    Ubuntu
Description:    Ubuntu 22.04.3 LTS
Release:    22.04
Codename:    jammy
-------------------------------------------

--- Kernel Version ---
$ uname -r
6.6.0
----------------------

[Alan-Jowett]

Can you try doing:

git submodule update --recursive --init 

This will clone the sub-repos.