Part 1 of #301908.
This renames the two versions of the Apple Public Source License seen in
nixpkgs; `apsl20` was often confused as being for the widely-used Apache
License 2.0.
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
