Do not special case supplementary import pathes

[nim-nim]

Let's just make the macros accept an unlimited number of -i flags

instead of trying to pack them in a single flag, which is less flexible and requires complex unpacking in the shell code

[ingvagabund]

https://github.com/gofed/go-macros/commit/9ea4573c11c1872f9b40b2a3fb7067a327fd98a9