[CMake] Pass -lpthread on FreeBSD.
[CMake] Pass -lpthread on FreeBSD.

At the time this code was originally written, Swift standard
library hasn't been ported to FreeBSD, so we didn't need any
additional library. This is not true anymore, so fix it.

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