Fix packaging the pcds env

[mrakitin]

The original build was missing the gcc compiler needed for the building of thriftpy2.
h/t @ZLLentz.

[mrakitin]

Checked the diffs, they look reasonable:

$ diff env-py39.yml ~/Downloads/pcds-5.8.2.yml
4d3
<   - pcds-tag
826c825
<       - git+https://github.com/slaclab/flask_authnz@0.0.24
---
>       - flask-authnz==0.0.24
846c845
<       - git+https://github.com/pcdshub/pmps-ui.git@v1.1.0
---
>       - pmpsui==1.1.0
868c867
< prefix: /cds/home/z/zlentz/miniconda3/envs/pcds-5.8.2
---
> prefix: /opt/conda/envs/pcds-5.8.2