add --lldb-test-swift-only flag to build script
add --lldb-test-swift-only flag to build script

This flag will be used by Swift PR checking to run just the
portion of the LLDB test suite that is specific to Swift.

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