flex: add missing ifdef magic to create/hide prototypes
flex: add missing ifdef magic to create/hide prototypes

This unbreaks build for some software with higher WARNS flags.

Reviewed by:	rpaulo
PR:		bin/139319 (parts already committed in previous revision)

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase