Checkpoint: Pipeline Arithmetic

Implement four small functions: 1. int expansion_math(void) — given #define TWICE(x) ((x) * 2) already in your editor, return TWICE(TWICE(3)) (12) and be able to say why it is not 18. 2. int link_outcome(int helper_is_static) — return 1 (undefined reference) if helper_is_static, else 0 (links). 3. int nm_visible(char letter) — return 1 iff the nm type letter denotes an externally visible symbol (T, D, B). 4. int archive_would_pull(int resolves_pending_ref) — return 1 iff the member resolves a pending undefined reference.