List of overridden environment variables for subprocesses to inherit.
Each element should be a string of the form ENVVARNAME=VALUE.
Entries in this list take precedence to those in the frame-local
environments. Therefore, let-binding `process-environment' is an easy
way to temporarily change the value of an environment variable,
irrespective of where it comes from. To use `process-environment' to
remove an environment variable, include only its name in the list,
This variable is set to nil when Emacs starts.
If multiple entries define the same variable, the first one always
Non-ASCII characters are encoded according to the initial value of
`locale-coding-system', i.e. the elements must normally be decoded for use. See `setenv' and `getenv'.