[build] Clean up lack of support of iOS device tests.
[build] Clean up lack of support of iOS device tests.

* Add --ios-all etc with a helpful error
  message for those who think it exists.
* Reject --ios --host-test early to avoid a cryptic
  "build target does not exist" error much later.

frootloops/swift,amraboelela/swift,allevato/swift,djwbrown/swift,JGiola/swift,tjw/swift,calebd/swift,benlangmuir/swift,practicalswift/swift,calebd/swift,frootloops/swift,benlangmuir/swift,practicalswift/swift,gribozavr/swift,arvedviehweger/swift,xedin/swift,glessard/swift,brentdax/swift,zisko/swift,deyton/swift,danielmartin/swift,djwbrown/swift,Jnosh/swift,jckarter/swift,calebd/swift,amraboelela/swift,felix91gr/swift,natecook1000/swift,devincoughlin/swift,karwa/swift,bitjammer/swift,atrick/swift,apple/swift,tinysun212/swift-windows,hughbe/swift,zisko/swift,austinzheng/swift,huonw/swift,tkremenek/swift,practicalswift/swift,sschiau/swift,djwbrown/swift,brentdax/swift,OscarSwanros/swift,calebd/swift,JGiola/swift,tkremenek/swift,hughbe/swift,swiftix/swift,codestergit/swift,allevato/swift,lorentey/swift,harlanhaskins/swift,tkremenek/swift,natecook1000/swift,tjw/swift,shahmishal/swift,alblue/swift,parkera/swift,glessard/swift,xedin/swift,rudkx/swift,OscarSwanros/swift,amraboelela/swift,Jnosh/swift,danielmartin/swift,OscarSwanros/swift,gribozavr/swift,airspeedswift/swift,deyton/swift,hughbe/swift,milseman/swift,danielmartin/swift,jckarter/swift,JGiola/swift,alblue/swift,sschiau/swift,return/swift,uasys/swift,danielmartin/swift,xwu/swift,lorentey/swift,return/swift,nathawes/swift,tjw/swift,brentdax/swift,CodaFi/swift,jckarter/swift,glessard/swift,uasys/swift,zisko/swift,frootloops/swift,roambotics/swift,return/swift,hooman/swift,lorentey/swift,manavgabhawala/swift,manavgabhawala/swift,jtbandes/swift,felix91gr/swift,alblue/swift,xedin/swift,shajrawi/swift,OscarSwanros/swift,harlanhaskins/swift,airspeedswift/swift,apple/swift,hughbe/swift,shajrawi/swift,airspeedswift/swift,Jnosh/swift,swiftix/swift,shajrawi/swift,hooman/swift,jopamer/swift,hooman/swift,gribozavr/swift,codestergit/swift,devincoughlin/swift,jtbandes/swift,jopamer/swift,swiftix/swift,benlangmuir/swift,parkera/swift,ahoppen/swift,nathawes/swift,devincoughlin/swift,karwa/swift,austinzheng/swift,natecook1000/swift,natecook1000/swift,airspeedswift/swift,natecook1000/swift,jopamer/swift,alblue/swift,arvedviehweger/swift,aschwaighofer/swift,devincoughlin/swift,codestergit/swift,stephentyrone/swift,jtbandes/swift,devincoughlin/swift,tinysun212/swift-windows,CodaFi/swift,jopamer/swift,rudkx/swift,aschwaighofer/swift,tinysun212/swift-windows,austinzheng/swift,arvedviehweger/swift,jopamer/swift,karwa/swift,zisko/swift,xedin/swift,uasys/swift,karwa/swift,amraboelela/swift,xwu/swift,parkera/swift,djwbrown/swift,nathawes/swift,harlanhaskins/swift,JGiola/swift,roambotics/swift,ahoppen/swift,nathawes/swift,jmgc/swift,jtbandes/swift,practicalswift/swift,karwa/swift,atrick/swift,manavgabhawala/swift,stephentyrone/swift,jmgc/swift,aschwaighofer/swift,atrick/swift,gregomni/swift,jmgc/swift,xwu/swift,felix91gr/swift,gribozavr/swift,calebd/swift,calebd/swift,natecook1000/swift,brentdax/swift,jtbandes/swift,glessard/swift,xedin/swift,hughbe/swift,swiftix/swift,CodaFi/swift,tkremenek/swift,return/swift,bitjammer/swift,glessard/swift,jtbandes/swift,glessard/swift,hughbe/swift,xedin/swift,practicalswift/swift,huonw/swift,sschiau/swift,ahoppen/swift,jckarter/swift,alblue/swift,codestergit/swift,arvedviehweger/swift,harlanhaskins/swift,xwu/swift,danielmartin/swift,return/swift,jckarter/swift,roambotics/swift,amraboelela/swift,xedin/swift,sschiau/swift,JGiola/swift,jmgc/swift,deyton/swift,hughbe/swift,atrick/swift,zisko/swift,stephentyrone/swift,hooman/swift,danielmartin/swift,deyton/swift,benlangmuir/swift,shajrawi/swift,devincoughlin/swift,sschiau/swift,uasys/swift,djwbrown/swift,hooman/swift,roambotics/swift,apple/swift,sschiau/swift,tjw/swift,tkremenek/swift,jckarter/swift,uasys/swift,shahmishal/swift,stephentyrone/swift,atrick/swift,tinysun212/swift-windows,djwbrown/swift,Jnosh/swift,bitjammer/swift,Jnosh/swift,practicalswift/swift,bitjammer/swift,huonw/swift,parkera/swift,nathawes/swift,jmgc/swift,gribozavr/swift,allevato/swift,apple/swift,shajrawi/swift,swiftix/swift,lorentey/swift,amraboelela/swift,zisko/swift,tinysun212/swift-windows,Jnosh/swift,milseman/swift,djwbrown/swift,rudkx/swift,milseman/swift,devincoughlin/swift,gregomni/swift,OscarSwanros/swift,brentdax/swift,bitjammer/swift,jtbandes/swift,gregomni/swift,rudkx/swift,sschiau/swift,nathawes/swift,benlangmuir/swift,sschiau/swift,milseman/swift,devincoughlin/swift,tinysun212/swift-windows,brentdax/swift,shahmishal/swift,allevato/swift,ahoppen/swift,deyton/swift,nathawes/swift,airspeedswift/swift,karwa/swift,calebd/swift,arvedviehweger/swift,gregomni/swift,huonw/swift,austinzheng/swift,manavgabhawala/swift,bitjammer/swift,rudkx/swift,hooman/swift,frootloops/swift,natecook1000/swift,tjw/swift,airspeedswift/swift,stephentyrone/swift,allevato/swift,harlanhaskins/swift,swiftix/swift,CodaFi/swift,felix91gr/swift,jopamer/swift,codestergit/swift,lorentey/swift,shahmishal/swift,manavgabhawala/swift,parkera/swift,shajrawi/swift,benlangmuir/swift,aschwaighofer/swift,lorentey/swift,karwa/swift,bitjammer/swift,tjw/swift,amraboelela/swift,OscarSwanros/swift,CodaFi/swift,xedin/swift,atrick/swift,jmgc/swift,CodaFi/swift,stephentyrone/swift,alblue/swift,stephentyrone/swift,frootloops/swift,shajrawi/swift,allevato/swift,roambotics/swift,ahoppen/swift,JGiola/swift,gregomni/swift,lorentey/swift,codestergit/swift,deyton/swift,apple/swift,aschwaighofer/swift,huonw/swift,airspeedswift/swift,jmgc/swift,austinzheng/swift,practicalswift/swift,felix91gr/swift,codestergit/swift,roambotics/swift,return/swift,CodaFi/swift,tkremenek/swift,practicalswift/swift,uasys/swift,tkremenek/swift,shahmishal/swift,danielmartin/swift,gribozavr/swift,milseman/swift,shahmishal/swift,gribozavr/swift,allevato/swift,hooman/swift,shajrawi/swift,lorentey/swift,karwa/swift,jopamer/swift,xwu/swift,return/swift,felix91gr/swift,alblue/swift,deyton/swift,austinzheng/swift,zisko/swift,Jnosh/swift,aschwaighofer/swift,shahmishal/swift,parkera/swift,manavgabhawala/swift,ahoppen/swift,gregomni/swift,xwu/swift,huonw/swift,felix91gr/swift,arvedviehweger/swift,manavgabhawala/swift,apple/swift,harlanhaskins/swift,xwu/swift,austinzheng/swift,tjw/swift,milseman/swift,brentdax/swift,jckarter/swift,parkera/swift,shahmishal/swift,gribozavr/swift,frootloops/swift,parkera/swift,rudkx/swift,tinysun212/swift-windows,frootloops/swift,arvedviehweger/swift,aschwaighofer/swift,swiftix/swift,milseman/swift,uasys/swift,harlanhaskins/swift,huonw/swift,OscarSwanros/swift