Revert "build-script: remove dead CMake options for Swift"
Revert "build-script: remove dead CMake options for Swift"

This reverts commit 95102bc258a6b30ba2349d561ef56ea48c601cae.

This is actually a dead option that is relied upon for some configurations. I am
going to add a note to not touch the option.

I talked with compnerd about this and they are cool with this.

I think that we can redo this in a nicer way when we are further into the
build-script-impl refactoring.

I added a note to the code to explain that it isn't dead.

rudkx/swift,tkremenek/swift,nathawes/swift,nathawes/swift,atrick/swift,rudkx/swift,glessard/swift,glessard/swift,nathawes/swift,hooman/swift,ahoppen/swift,atrick/swift,xwu/swift,nathawes/swift,parkera/swift,apple/swift,xwu/swift,JGiola/swift,benlangmuir/swift,tkremenek/swift,atrick/swift,rudkx/swift,xwu/swift,glessard/swift,parkera/swift,tkremenek/swift,jmgc/swift,tkremenek/swift,parkera/swift,jmgc/swift,benlangmuir/swift,ahoppen/swift,jmgc/swift,rudkx/swift,rudkx/swift,roambotics/swift,gregomni/swift,JGiola/swift,JGiola/swift,apple/swift,tkremenek/swift,jmgc/swift,apple/swift,tkremenek/swift,JGiola/swift,atrick/swift,hooman/swift,apple/swift,parkera/swift,parkera/swift,parkera/swift,tkremenek/swift,roambotics/swift,gregomni/swift,jmgc/swift,gregomni/swift,benlangmuir/swift,xwu/swift,xwu/swift,ahoppen/swift,nathawes/swift,gregomni/swift,parkera/swift,hooman/swift,jmgc/swift,roambotics/swift,atrick/swift,apple/swift,ahoppen/swift,apple/swift,hooman/swift,benlangmuir/swift,hooman/swift,glessard/swift,ahoppen/swift,nathawes/swift,roambotics/swift,JGiola/swift,atrick/swift,gregomni/swift,jmgc/swift,hooman/swift,xwu/swift,JGiola/swift,benlangmuir/swift,roambotics/swift,hooman/swift,rudkx/swift,xwu/swift,glessard/swift,ahoppen/swift,nathawes/swift,glessard/swift,benlangmuir/swift,gregomni/swift,parkera/swift,roambotics/swift