[Threading][Windows] Fix another Windows niggle.
[Threading][Windows] Fix another Windows niggle.

Looks like I forgot to update the Win32.h implementation.

rdar://90776105

glessard/swift,JGiola/swift,apple/swift,JGiola/swift,roambotics/swift,apple/swift,apple/swift,JGiola/swift,roambotics/swift,benlangmuir/swift,glessard/swift,benlangmuir/swift,JGiola/swift,benlangmuir/swift,benlangmuir/swift,JGiola/swift,roambotics/swift,roambotics/swift,apple/swift,roambotics/swift,glessard/swift,benlangmuir/swift,roambotics/swift,benlangmuir/swift,glessard/swift,glessard/swift,apple/swift,JGiola/swift,apple/swift,glessard/swift