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
Well, it wasn't really broken, just emitting a zillion narrowing
warnings in generated code. Apparently "-Wno-narrowing" is how the
modern compilers like you to ask them to tone it down.
