[Threading][Windows] Undefine Yield and ERROR.
[Threading][Windows] Undefine Yield and ERROR.

`windows.h` defines a couple of very unhelpfully named macros.
Undefine them after including it.

rdar://90776105

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