Errors during ./ns3 build procedure about ns3-gym

[sv1ple]

As a temporary workaround, I deleted the examples/interference-pattern folder and removed the reference from CMakeLists.txt (check below)
Now, ns3 is built successfully and I am able to run the opengym example properly.

New CMakeLists.txt without interference-pattern:

build_lib_example(
  NAME linear-mesh
  SOURCE_FILES linear-mesh/sim.cc
  LIBRARIES_TO_LINK
    ${libapplications}
    ${libcore}
    ${libinternet}
    ${libopengym}
    ${libwifi}
)

build_lib_example(
  NAME linear-mesh-2
  SOURCE_FILES linear-mesh-2/sim.cc
               linear-mesh-2/mygym.cc
  LIBRARIES_TO_LINK
    ${libapplications}
    ${libcore}
    ${libinternet}
    ${libopengym}
    ${libwifi}
)

build_lib_example(
  NAME opengym
  SOURCE_FILES opengym/sim.cc
  LIBRARIES_TO_LINK
    ${libcore}
    ${libopengym}
)

build_lib_example(
  NAME opengym-2
  SOURCE_FILES opengym-2/sim.cc
               opengym-2/mygym.cc
  LIBRARIES_TO_LINK
    ${libcore}
    ${libopengym}
)

build_lib_example(
  NAME rl-tcp
  SOURCE_FILES rl-tcp/sim.cc
               rl-tcp/tcp-rl-env.cc
               rl-tcp/tcp-rl.cc
  LIBRARIES_TO_LINK
    ${libapplications}
    ${libcore}
    ${libflow-monitor}
    ${libinternet}
    ${libopengym}
    ${libpoint-to-point-layout}
    ${libptp}
)