[ConstraintSystem] NFC: Warn if result of `generate*` is unused
[ConstraintSystem] NFC: Warn if result of `generate*` is unused

Not checking success of constraint generation could lead to crashes
e.g. when follow-up code accesses something that hasn't been processed
due to error.

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