Some cleanups for https://github.com/fontforge/fontforge/pull/1843 and other

This has some other cleanups to bring down warning message sizes too
I don't understand why this is a hard choice: there's a library-defined symbolic constant, we should use it. Giving it another name will just create confusion. The names in czmq are cleanly prefixed, so there shouldn't be any clash with other 3rd-party libraries or Fontforge code.