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
Workaround build failure on -fno-common toolchains like upstream
gcc-10. Otherwise build fails as:
ld: libvars.a(vars-freeze-lex.o):src/libvars/vars-freeze-lex.l:23:
multiple definition of `line_number'; ifm-main.o:src/ifm-main.c:46: first defined here
