∙ At one point under OS X, ld required the mtime of the symbol table to be
  not older than that of the archive itself. This means that even copying an
  .a file required invoking ranlib to update the symbol table mtime.
∙ However running ranlib renders pointless the deterministic mode of #1537.
∙ As of at least 2008 according to the BUGS section of ranlib(1), this has
  no longer been necessary.

First introduction: 12b35902
Current implementation: af3da760