bug#78377: Cross-Compile - "src/make-prime-list: cannot execute: required file not found"

It'd be nice to be able to cross-compile coreutils.

It could be done by detecting if `--host=` is different from the build system.
If it is different, then make the `src/primes.h` target natively
(specifically the `src/make-prime-list` target).

I noticed it was a very old issue (going back to 2012).
My workaround was just to `configure` without any arguments, `make
src/primes.h`, then `configure` again for cross-compiling, and run a
normal `make`.