As discussed on d-devel@l.d.o [*], it would be nice to remove the
getenv/putenv usage from the lib itself (move the functionalities to
the command lines). Quotes:

[...]

getenv is, yes, but it is not protected against concurrent calls to
setenv/putenv. So there are thread safety concerns here indeed.

[...]

[*]https://lists.debian.org/debian-devel/2015/02/msg00149.html