[build-script] Build & test XCTest (on OS X, too)
[build-script] Build & test XCTest (on OS X, too)

Allow swift-corelibs-xctest to be built and tested on Linux and OS X,
via `utils/build-script --xctest --test`.

On OS X, XCTest is built via `xcodebuild`, which has been possible since
https://github.com/apple/swift-corelibs-xctest/pull/47. It's tested via
the "SwiftXCTestFunctionalTests" Xcode target. Keep in mind that
`xcodebuild` must be configured on the host machine to use a Swift
toolchain that can build XCTest--as of
https://github.com/apple/swift-corelibs-xctest/pull/48, that would be
`swift-DEVELOPMENT-SNAPSHOT-2016-02-08` or later.

On Linux, XCTest is built and tested via the project's
`build_script.py`, which has been possible since
https://github.com/apple/swift-corelibs-xctest/pull/46.

jtbandes/swift,xedin/swift,hughbe/swift,tinysun212/swift-windows,benlangmuir/swift,apple/swift,jopamer/swift,alblue/swift,roambotics/swift,glessard/swift,jmgc/swift,hughbe/swift,rudkx/swift,zisko/swift,devincoughlin/swift,karwa/swift,karwa/swift,harlanhaskins/swift,KrishMunot/swift,gribozavr/swift,benlangmuir/swift,xwu/swift,stephentyrone/swift,modocache/swift,practicalswift/swift,brentdax/swift,bitjammer/swift,Jnosh/swift,practicalswift/swift,swiftix/swift,johnno1962d/swift,allevato/swift,KrishMunot/swift,djwbrown/swift,gmilos/swift,devincoughlin/swift,tkremenek/swift,bitjammer/swift,djwbrown/swift,dduan/swift,jmgc/swift,austinzheng/swift,tjw/swift,aschwaighofer/swift,kperryua/swift,tjw/swift,lorentey/swift,arvedviehweger/swift,SwiftAndroid/swift,jtbandes/swift,parkera/swift,benlangmuir/swift,tardieu/swift,tinysun212/swift-windows,danielmartin/swift,hooman/swift,alblue/swift,alblue/swift,frootloops/swift,therealbnut/swift,zisko/swift,bitjammer/swift,tjw/swift,amraboelela/swift,frootloops/swift,harlanhaskins/swift,glessard/swift,roambotics/swift,allevato/swift,codestergit/swift,arvedviehweger/swift,sschiau/swift,arvedviehweger/swift,danielmartin/swift,sschiau/swift,Jnosh/swift,devincoughlin/swift,danielmartin/swift,harlanhaskins/swift,hooman/swift,stephentyrone/swift,xwu/swift,djwbrown/swift,swiftix/swift,dduan/swift,jckarter/swift,shahmishal/swift,johnno1962d/swift,rudkx/swift,milseman/swift,OscarSwanros/swift,deyton/swift,djwbrown/swift,harlanhaskins/swift,kperryua/swift,alblue/swift,xwu/swift,hooman/swift,austinzheng/swift,jmgc/swift,shahmishal/swift,calebd/swift,gribozavr/swift,rudkx/swift,huonw/swift,karwa/swift,atrick/swift,codestergit/swift,shahmishal/swift,IngmarStein/swift,ken0nek/swift,kstaring/swift,jmgc/swift,milseman/swift,CodaFi/swift,kperryua/swift,kperryua/swift,aschwaighofer/swift,ahoppen/swift,djwbrown/swift,practicalswift/swift,nathawes/swift,calebd/swift,uasys/swift,modocache/swift,nathawes/swift,shajrawi/swift,stephentyrone/swift,harlanhaskins/swift,KrishMunot/swift,manavgabhawala/swift,frootloops/swift,sschiau/swift,brentdax/swift,jckarter/swift,austinzheng/swift,OscarSwanros/swift,manavgabhawala/swift,swiftix/swift,devincoughlin/swift,jopamer/swift,gottesmm/swift,dduan/swift,brentdax/swift,tardieu/swift,uasys/swift,KrishMunot/swift,natecook1000/swift,johnno1962d/swift,practicalswift/swift,natecook1000/swift,gmilos/swift,ben-ng/swift,KrishMunot/swift,russbishop/swift,shajrawi/swift,dduan/swift,JaSpa/swift,austinzheng/swift,russbishop/swift,deyton/swift,ahoppen/swift,modocache/swift,practicalswift/swift,lorentey/swift,parkera/swift,deyton/swift,IngmarStein/swift,kstaring/swift,hooman/swift,felix91gr/swift,sschiau/swift,shahmishal/swift,swiftix/swift,milseman/swift,KrishMunot/swift,hooman/swift,codestergit/swift,SwiftAndroid/swift,zisko/swift,amraboelela/swift,airspeedswift/swift,CodaFi/swift,amraboelela/swift,kstaring/swift,swiftix/swift,modocache/swift,OscarSwanros/swift,benlangmuir/swift,jtbandes/swift,codestergit/swift,zisko/swift,shajrawi/swift,xwu/swift,benlangmuir/swift,return/swift,xedin/swift,tardieu/swift,arvedviehweger/swift,hooman/swift,roambotics/swift,deyton/swift,kperryua/swift,gottesmm/swift,glessard/swift,huonw/swift,manavgabhawala/swift,gregomni/swift,russbishop/swift,airspeedswift/swift,nathawes/swift,devincoughlin/swift,IngmarStein/swift,danielmartin/swift,tardieu/swift,practicalswift/swift,calebd/swift,tkremenek/swift,felix91gr/swift,uasys/swift,CodaFi/swift,tinysun212/swift-windows,tinysun212/swift-windows,return/swift,ben-ng/swift,lorentey/swift,aschwaighofer/swift,ben-ng/swift,karwa/swift,stephentyrone/swift,ken0nek/swift,huonw/swift,djwbrown/swift,Jnosh/swift,atrick/swift,JGiola/swift,felix91gr/swift,JaSpa/swift,atrick/swift,modocache/swift,dreamsxin/swift,aschwaighofer/swift,hughbe/swift,apple/swift,sschiau/swift,apple/swift,austinzheng/swift,gribozavr/swift,frootloops/swift,frootloops/swift,IngmarStein/swift,alblue/swift,kstaring/swift,karwa/swift,codestergit/swift,natecook1000/swift,CodaFi/swift,calebd/swift,therealbnut/swift,gmilos/swift,CodaFi/swift,bitjammer/swift,Jnosh/swift,tjw/swift,ben-ng/swift,stephentyrone/swift,harlanhaskins/swift,SwiftAndroid/swift,shajrawi/swift,gribozavr/swift,gregomni/swift,atrick/swift,JGiola/swift,apple/swift,gribozavr/swift,gribozavr/swift,austinzheng/swift,xwu/swift,KrishMunot/swift,ken0nek/swift,stephentyrone/swift,frootloops/swift,russbishop/swift,arvedviehweger/swift,SwiftAndroid/swift,amraboelela/swift,russbishop/swift,johnno1962d/swift,apple/swift,uasys/swift,gottesmm/swift,JaSpa/swift,manavgabhawala/swift,jckarter/swift,austinzheng/swift,karwa/swift,tardieu/swift,jckarter/swift,jopamer/swift,jckarter/swift,hughbe/swift,gmilos/swift,jmgc/swift,practicalswift/swift,OscarSwanros/swift,johnno1962d/swift,lorentey/swift,arvedviehweger/swift,lorentey/swift,swiftix/swift,JaSpa/swift,bitjammer/swift,calebd/swift,tjw/swift,russbishop/swift,IngmarStein/swift,JGiola/swift,jopamer/swift,nathawes/swift,danielmartin/swift,therealbnut/swift,lorentey/swift,deyton/swift,uasys/swift,hughbe/swift,gottesmm/swift,ken0nek/swift,aschwaighofer/swift,tinysun212/swift-windows,SwiftAndroid/swift,gottesmm/swift,danielmartin/swift,alblue/swift,brentdax/swift,ahoppen/swift,tkremenek/swift,ahoppen/swift,bitjammer/swift,dreamsxin/swift,brentdax/swift,huonw/swift,ben-ng/swift,return/swift,rudkx/swift,allevato/swift,calebd/swift,xedin/swift,airspeedswift/swift,milseman/swift,return/swift,jopamer/swift,tkremenek/swift,gmilos/swift,ken0nek/swift,shajrawi/swift,tjw/swift,hooman/swift,calebd/swift,xedin/swift,ken0nek/swift,natecook1000/swift,russbishop/swift,lorentey/swift,gottesmm/swift,parkera/swift,sschiau/swift,JGiola/swift,benlangmuir/swift,parkera/swift,therealbnut/swift,arvedviehweger/swift,tinysun212/swift-windows,OscarSwanros/swift,jmgc/swift,JGiola/swift,JaSpa/swift,airspeedswift/swift,parkera/swift,hughbe/swift,sschiau/swift,tardieu/swift,felix91gr/swift,natecook1000/swift,zisko/swift,zisko/swift,therealbnut/swift,deyton/swift,apple/swift,bitjammer/swift,devincoughlin/swift,xwu/swift,glessard/swift,jtbandes/swift,kperryua/swift,manavgabhawala/swift,milseman/swift,tkremenek/swift,ben-ng/swift,ken0nek/swift,therealbnut/swift,parkera/swift,gregomni/swift,amraboelela/swift,airspeedswift/swift,dduan/swift,brentdax/swift,frootloops/swift,xwu/swift,shajrawi/swift,Jnosh/swift,manavgabhawala/swift,devincoughlin/swift,gottesmm/swift,OscarSwanros/swift,glessard/swift,tkremenek/swift,johnno1962d/swift,practicalswift/swift,xedin/swift,allevato/swift,IngmarStein/swift,rudkx/swift,tinysun212/swift-windows,amraboelela/swift,nathawes/swift,milseman/swift,milseman/swift,rudkx/swift,xedin/swift,shahmishal/swift,codestergit/swift,tjw/swift,alblue/swift,uasys/swift,djwbrown/swift,johnno1962d/swift,gregomni/swift,xedin/swift,devincoughlin/swift,parkera/swift,lorentey/swift,jtbandes/swift,CodaFi/swift,gmilos/swift,kstaring/swift,ahoppen/swift,therealbnut/swift,nathawes/swift,gregomni/swift,danielmartin/swift,sschiau/swift,aschwaighofer/swift,huonw/swift,tardieu/swift,SwiftAndroid/swift,manavgabhawala/swift,JaSpa/swift,return/swift,gmilos/swift,IngmarStein/swift,gregomni/swift,modocache/swift,atrick/swift,ben-ng/swift,jopamer/swift,tkremenek/swift,deyton/swift,allevato/swift,allevato/swift,felix91gr/swift,jckarter/swift,SwiftAndroid/swift,karwa/swift,karwa/swift,brentdax/swift,shahmishal/swift,ahoppen/swift,natecook1000/swift,felix91gr/swift,roambotics/swift,glessard/swift,kstaring/swift,natecook1000/swift,JaSpa/swift,Jnosh/swift,shajrawi/swift,Jnosh/swift,zisko/swift,jtbandes/swift,CodaFi/swift,JGiola/swift,felix91gr/swift,amraboelela/swift,allevato/swift,jckarter/swift,gribozavr/swift,return/swift,codestergit/swift,dduan/swift,hughbe/swift,huonw/swift,return/swift,swiftix/swift,roambotics/swift,airspeedswift/swift,jmgc/swift,nathawes/swift,shajrawi/swift,jtbandes/swift,xedin/swift,roambotics/swift,huonw/swift,shahmishal/swift,aschwaighofer/swift,dduan/swift,modocache/swift,stephentyrone/swift,uasys/swift,gribozavr/swift,jopamer/swift,OscarSwanros/swift,harlanhaskins/swift,shahmishal/swift,kstaring/swift,parkera/swift,kperryua/swift,atrick/swift,airspeedswift/swift