gyb: use a stable hash for Syntax
gyb: use a stable hash for Syntax

This changes the hash from the Python `hash` function to SHA1.  Python 3
adopted SIP as the hashing algorithm which changed the hash results.  We
could no longer use a different python interpreter across the builds.  A
stable hashing algorithm allows easier migration.

jmgc/swift,xwu/swift,jckarter/swift,roambotics/swift,CodaFi/swift,xwu/swift,allevato/swift,atrick/swift,CodaFi/swift,ahoppen/swift,xwu/swift,ahoppen/swift,stephentyrone/swift,nathawes/swift,glessard/swift,xwu/swift,hooman/swift,roambotics/swift,ahoppen/swift,benlangmuir/swift,gregomni/swift,apple/swift,CodaFi/swift,glessard/swift,atrick/swift,glessard/swift,roambotics/swift,rudkx/swift,atrick/swift,tkremenek/swift,CodaFi/swift,glessard/swift,JGiola/swift,allevato/swift,jckarter/swift,rudkx/swift,parkera/swift,JGiola/swift,airspeedswift/swift,stephentyrone/swift,JGiola/swift,xwu/swift,allevato/swift,apple/swift,allevato/swift,atrick/swift,stephentyrone/swift,parkera/swift,jckarter/swift,gregomni/swift,nathawes/swift,ahoppen/swift,nathawes/swift,atrick/swift,jmgc/swift,parkera/swift,jckarter/swift,CodaFi/swift,xwu/swift,hooman/swift,nathawes/swift,rudkx/swift,glessard/swift,glessard/swift,hooman/swift,parkera/swift,stephentyrone/swift,nathawes/swift,parkera/swift,allevato/swift,rudkx/swift,roambotics/swift,ahoppen/swift,xwu/swift,gregomni/swift,stephentyrone/swift,ahoppen/swift,hooman/swift,jmgc/swift,JGiola/swift,apple/swift,rudkx/swift,jmgc/swift,benlangmuir/swift,jmgc/swift,benlangmuir/swift,gregomni/swift,airspeedswift/swift,jckarter/swift,roambotics/swift,JGiola/swift,roambotics/swift,jckarter/swift,jmgc/swift,apple/swift,CodaFi/swift,tkremenek/swift,parkera/swift,tkremenek/swift,hooman/swift,apple/swift,airspeedswift/swift,benlangmuir/swift,CodaFi/swift,airspeedswift/swift,gregomni/swift,tkremenek/swift,tkremenek/swift,JGiola/swift,stephentyrone/swift,airspeedswift/swift,hooman/swift,apple/swift,parkera/swift,airspeedswift/swift,rudkx/swift,airspeedswift/swift,allevato/swift,allevato/swift,nathawes/swift,benlangmuir/swift,tkremenek/swift,benlangmuir/swift,jckarter/swift,tkremenek/swift,nathawes/swift,jmgc/swift,gregomni/swift,parkera/swift,hooman/swift,stephentyrone/swift,atrick/swift