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
Originally enabled in
950261bb9a ('darwin: fix gtk+3 dependencies')
since then many dependencies may have been changed to rely on Cocoa
only. Let's try disabling it by default to avoid the mesa dependency
on darwin, we can always enable on a case-by-case basis for apps that
really use X11.
