Commit Briefs
Revert "Remove __linux__ shim" (neels/wip2)
This reverts commit 4db88d74a79c9f7a3b792d21e337d36621a2370a.
Fix macro diff_atom_*idx return value types
The macros sometimes returned unsigned int (atoms.len) or long int ((ATOM) - head). Make that always unsigned int, with some range checks against negative values.