Rather than `$BASH`, `glibc` now hardcodes `/bin/bash` as
interpreter[1] in several scripts (including `ldd`).
This is a problem because relevant programs such as `ldd(1)` won't work
properly without this since we set `BASH` to `/bin/sh` to avoid
dependencies to the bootstrap tools for `bash` as runtime-dependency (since
NixOS doesn't have `/bin/bash`).
Considering that this was only done as an "improvement" to their
build-system and not because they wanted to use some bashisms here (the
variable was always called `BASH` and we still used `/bin/sh` anyways),
I'd consider this to be relatively safe.
[1] 5188a9d0265cc6f7235a8af1d31ab02e4a24853d
