You are right Joesph Smith did say that a temple would be built in Zion in his generation (D&C 84:8).  
 
Let's look at a prophesy of Christ in Luke 21:31-32 "So likewise ye, when ye see these things come to pass, know ye that the kingdom of God is nigh at hand. Verily I say unto you, This generation shall not pass away, till all be fulfilled." 
 
Here Christ says that all things pertaining to the return of Christ shall be fulfilled in the Apostles generation.  
 
So is Christ a false prophet too? 
 
Obviously not! The only logical solution is that Christ does not mean a generation in the terms of man but is referring to the entirety of mankind as a generation. Which makes sense from a celestial position since Christ is eternal and all the generations of man are insignificant in the scope of eternity.  
 
Thank you for your question I hope that I was able to answer it well!