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
This issue is fixed in upstream OpenOCD, but there hasn't been a
new release since the fix.
See https://github.com/libusb/libusb/issues/928 for context.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
