Failing Hydra build: https://hydra.nixos.org/build/230518081
So apparently `vasprintf`, `asprintf` are now available by default, not
just with `_GNU_SOURCE` and now `mamba` (or to be precise, its
dependency `xputty`) fails like this:
../xputty/xfilepicker.c:225:5: error: format not a string literal and no format arguments [-Werror=format-security]
225 | asprintf(&filepicker->path, path);
| ^~~~~~~~
It seems as if now that these functions are available by default, the
format-security check from gcc actually works.