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
Without the change the build against upstream gcc-10 build fails as:
ld: sprite.o:/build/0verkill/data.h:171: multiple definition of `obj_attr'; server.o:/build/0verkill/data.h:171: first defined here
ld: sprite.o:/build/0verkill/data.h:142: multiple definition of `weapon_name'; server.o:/build/0verkill/data.h:142: first defined here
Use -fcommon as a workeround until upstream updates the code.
