CDT `mesa-libgl` missing some requirements

[jakirkham]

The CDT mesa-libgl seems to be missing some requirements. So have had to add them manually when using it. However it would be nice if it pulled in other CDTs needed automatically. FWICT that list should include the following.

    - {{ cdt('libselinux') }}        # [linux]
    - {{ cdt('libxcb') }}            # [linux]
    - {{ cdt('libxdamage') }}        # [linux]
    - {{ cdt('libxfixes') }}         # [linux]
    - {{ cdt('libxxf86vm') }}        # [linux]

Snippet about missing library dependencies below. Link to the associated log afterwards.

/home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../lib/gcc/x86_64-conda_cos6-linux-gnu/7.3.0/../../../../x86_64-conda_cos6-linux-gnu/bin/ld: warning: libselinux.so.1, needed by /home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../x86_64-conda_cos6-linux-gnu/sysroot/usr/lib64/libGL.so, not found (try using -rpath or -rpath-link)
/home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../lib/gcc/x86_64-conda_cos6-linux-gnu/7.3.0/../../../../x86_64-conda_cos6-linux-gnu/bin/ld: warning: libXdamage.so.1, needed by /home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../x86_64-conda_cos6-linux-gnu/sysroot/usr/lib64/libGL.so, not found (try using -rpath or -rpath-link)
/home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../lib/gcc/x86_64-conda_cos6-linux-gnu/7.3.0/../../../../x86_64-conda_cos6-linux-gnu/bin/ld: warning: libXfixes.so.3, needed by /home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../x86_64-conda_cos6-linux-gnu/sysroot/usr/lib64/libGL.so, not found (try using -rpath or -rpath-link)
/home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../lib/gcc/x86_64-conda_cos6-linux-gnu/7.3.0/../../../../x86_64-conda_cos6-linux-gnu/bin/ld: warning: libxcb-glx.so.0, needed by /home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../x86_64-conda_cos6-linux-gnu/sysroot/usr/lib64/libGL.so, not found (try using -rpath or -rpath-link)
/home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../lib/gcc/x86_64-conda_cos6-linux-gnu/7.3.0/../../../../x86_64-conda_cos6-linux-gnu/bin/ld: warning: libxcb-dri2.so.0, needed by /home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../x86_64-conda_cos6-linux-gnu/sysroot/usr/lib64/libGL.so, not found (try using -rpath or -rpath-link)
/home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../lib/gcc/x86_64-conda_cos6-linux-gnu/7.3.0/../../../../x86_64-conda_cos6-linux-gnu/bin/ld: warning: libXxf86vm.so.1, needed by /home/conda/feedstock_root/build_artifacts/glew_1546219221094/_build_env/bin/../x86_64-conda_cos6-linux-gnu/sysroot/usr/lib64/libGL.so, not found (try using -rpath or -rpath-link)

ref: https://circleci.com/gh/conda-forge/glew-feedstock/40

[jakirkham]

Thoughts on this?