build: create a helper function to define custom targets
build: create a helper function to define custom targets

Replace the duplicated logic for defining the targets for the standard
library variants with a call to a function that creates the targets.
This allows us to easily add variants of the standard library without
having to track all the sites for the name.

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