[CodeCompletion] Forward declare types in constraints instead of importing ConstraintSystem.h
[CodeCompletion] Forward declare types in constraints instead of importing ConstraintSystem.h

Importing ConstraintSystem.h caused some build failures on Windows while building LLDB (which incidentally is also importing IDETypeChecking.h). Forward declare them to work around the build failure.

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