Failed: conda build . -m .ci_support/linux_python3.8.____cpython.yaml

Hi @looooo

I am creating an AppImage for Linux using docker and getting below errors:

Logs of `conda build . -m .ci_support/linux_python3.8.____cpython.yaml`: https://paste.ubuntu.com/p/sk2DK3BKv4/

CMakeError.log: https://paste.ubuntu.com/p/rChRWNYBGJ/

From errors, it looks like CMake unable to found lpthreads. Do, I have to create any symbolic link (`ln -s`) inside a docker container.

### Steps I followed:

1. Clone https://github.com/looooo/freecad-feedstock.
1. Run `sudo docker run -i -t -v ~/projects/:/home/conda/projects --name conda-forge condaforge/linux-anvil-comp7` command. Here in `~/projects/` folder I have freecad-feedstock.
1. After entering into docker shell, I run `/usr/bin/sudo yum install -y mesa-libGL-devel` command.
1. Also, run `conda update --all` command.
1. Go the freecad-feedstock directory (`cd ~/projects/freecad-feedstock`).
1. Run `conda build . -m .ci_support/linux_python3.8.____cpython.yaml` command.

Source: https://github.com/FreeCAD/FreeCAD_Conda/blob/master/build.md#linux

On debugging, I found that process failed at `cmake` command. (https://github.com/looooo/freecad-feedstock/blob/master/recipe/build.sh#L38)

Before three months, I was successfully able to create an AppImage (https://github.com/FreeCAD/FreeCAD_Conda/issues/38) by following same above procedure.

Thanks in advance!

Start with the Linux procedure in build.md and reproduce `conda build . -m .ci_support/linux_python3.8.____cpython.yaml` in the described Docker container. Inspect recipe/build.sh at line 38, the `.ci_support` configuration, and the linked CMake logs. Done means the FreeCAD recipe builds successfully without the reported pthread-related failure.

Written by the indexing model from the issue text.