with structuredAttrs lists will be bash arrays which cannot be exported
which will be a issue with some patches and some wrappers like cc-wrapper
this makes it clearer that NIX_CFLAGS_COMPILE must be a string as lists
in env cause a eval failure
mkDerivation doesn't do anything with this,
and while it does become an environment variable
AFAICT that was never the intention and isn't helpful here.