[build-script] Move some calculations into independent methods.
[build-script] Move some calculations into independent methods.

Move the calculations of platforms_to_skip_build, platforms_to_skip_test, platforms_archs_to_skip_test, and platforms_to_skip_test_host to their own independent functions. Each function deal with one of them and they are pure functions, which should improve readability a little.

karwa/swift,atrick/swift,karwa/swift,benlangmuir/swift,roambotics/swift,devincoughlin/swift,shajrawi/swift,devincoughlin/swift,airspeedswift/swift,jmgc/swift,atrick/swift,atrick/swift,shajrawi/swift,stephentyrone/swift,ahoppen/swift,glessard/swift,harlanhaskins/swift,JGiola/swift,shajrawi/swift,nathawes/swift,ahoppen/swift,CodaFi/swift,stephentyrone/swift,gribozavr/swift,apple/swift,xedin/swift,gribozavr/swift,xedin/swift,hooman/swift,parkera/swift,gregomni/swift,lorentey/swift,benlangmuir/swift,benlangmuir/swift,karwa/swift,jckarter/swift,jckarter/swift,xwu/swift,ahoppen/swift,stephentyrone/swift,JGiola/swift,aschwaighofer/swift,atrick/swift,CodaFi/swift,nathawes/swift,harlanhaskins/swift,gribozavr/swift,glessard/swift,sschiau/swift,parkera/swift,airspeedswift/swift,aschwaighofer/swift,allevato/swift,benlangmuir/swift,xwu/swift,jckarter/swift,aschwaighofer/swift,CodaFi/swift,glessard/swift,xedin/swift,nathawes/swift,rudkx/swift,allevato/swift,benlangmuir/swift,karwa/swift,shahmishal/swift,jmgc/swift,jckarter/swift,airspeedswift/swift,xedin/swift,jmgc/swift,nathawes/swift,jckarter/swift,airspeedswift/swift,lorentey/swift,xwu/swift,sschiau/swift,lorentey/swift,karwa/swift,gregomni/swift,xwu/swift,rudkx/swift,nathawes/swift,allevato/swift,hooman/swift,aschwaighofer/swift,stephentyrone/swift,atrick/swift,shahmishal/swift,apple/swift,allevato/swift,tkremenek/swift,harlanhaskins/swift,CodaFi/swift,shahmishal/swift,nathawes/swift,tkremenek/swift,xedin/swift,jckarter/swift,lorentey/swift,rudkx/swift,gregomni/swift,sschiau/swift,devincoughlin/swift,karwa/swift,tkremenek/swift,rudkx/swift,xedin/swift,aschwaighofer/swift,gregomni/swift,shajrawi/swift,xwu/swift,xedin/swift,stephentyrone/swift,shajrawi/swift,sschiau/swift,shahmishal/swift,hooman/swift,nathawes/swift,roambotics/swift,apple/swift,ahoppen/swift,ahoppen/swift,jmgc/swift,gribozavr/swift,shahmishal/swift,shajrawi/swift,devincoughlin/swift,roambotics/swift,parkera/swift,gribozavr/swift,roambotics/swift,shajrawi/swift,parkera/swift,apple/swift,hooman/swift,karwa/swift,benlangmuir/swift,JGiola/swift,shahmishal/swift,lorentey/swift,harlanhaskins/swift,gregomni/swift,parkera/swift,sschiau/swift,allevato/swift,hooman/swift,parkera/swift,gribozavr/swift,aschwaighofer/swift,roambotics/swift,sschiau/swift,lorentey/swift,jmgc/swift,JGiola/swift,JGiola/swift,apple/swift,shajrawi/swift,rudkx/swift,devincoughlin/swift,airspeedswift/swift,CodaFi/swift,airspeedswift/swift,glessard/swift,glessard/swift,sschiau/swift,tkremenek/swift,JGiola/swift,aschwaighofer/swift,hooman/swift,devincoughlin/swift,gribozavr/swift,shahmishal/swift,parkera/swift,lorentey/swift,CodaFi/swift,gregomni/swift,allevato/swift,stephentyrone/swift,xwu/swift,allevato/swift,xedin/swift,stephentyrone/swift,CodaFi/swift,jmgc/swift,rudkx/swift,devincoughlin/swift,parkera/swift,gribozavr/swift,harlanhaskins/swift,devincoughlin/swift,lorentey/swift,atrick/swift,apple/swift,harlanhaskins/swift,tkremenek/swift,jmgc/swift,airspeedswift/swift,xwu/swift,jckarter/swift,hooman/swift,roambotics/swift,tkremenek/swift,shahmishal/swift,sschiau/swift,karwa/swift,tkremenek/swift,glessard/swift,harlanhaskins/swift,ahoppen/swift