[Concurrency] Move debug-only pthread code into the debug-only #ifdef (#41278)
[Concurrency] Move debug-only pthread code into the debug-only #ifdef (#41278)


atrick/swift,glessard/swift,atrick/swift,ahoppen/swift,apple/swift,rudkx/swift,atrick/swift,atrick/swift,JGiola/swift,glessard/swift,apple/swift,rudkx/swift,roambotics/swift,rudkx/swift,JGiola/swift,atrick/swift,roambotics/swift,JGiola/swift,glessard/swift,ahoppen/swift,glessard/swift,apple/swift,rudkx/swift,rudkx/swift,benlangmuir/swift,roambotics/swift,JGiola/swift,JGiola/swift,gregomni/swift,benlangmuir/swift,atrick/swift,apple/swift,gregomni/swift,apple/swift,benlangmuir/swift,rudkx/swift,ahoppen/swift,apple/swift,roambotics/swift,ahoppen/swift,ahoppen/swift,gregomni/swift,benlangmuir/swift,benlangmuir/swift,glessard/swift,roambotics/swift,roambotics/swift,JGiola/swift,ahoppen/swift,benlangmuir/swift,gregomni/swift,gregomni/swift,glessard/swift,gregomni/swift