AST: fix build with newer clang
AST: fix build with newer clang

Elaborate the `NodeKind` typename to avoid ambiguity with `llvm::yaml::NodeKind`
and `swift::experimental_dependencies::NodeKind`.  This fixes the build with
newer compilers.

practicalswift/swift,gregomni/swift,shahmishal/swift,parkera/swift,practicalswift/swift,xedin/swift,CodaFi/swift,gregomni/swift,devincoughlin/swift,rudkx/swift,airspeedswift/swift,atrick/swift,benlangmuir/swift,xedin/swift,harlanhaskins/swift,nathawes/swift,parkera/swift,shajrawi/swift,tkremenek/swift,nathawes/swift,parkera/swift,glessard/swift,sschiau/swift,gribozavr/swift,xedin/swift,ahoppen/swift,atrick/swift,glessard/swift,gregomni/swift,shahmishal/swift,devincoughlin/swift,airspeedswift/swift,airspeedswift/swift,hooman/swift,stephentyrone/swift,lorentey/swift,devincoughlin/swift,practicalswift/swift,jmgc/swift,hooman/swift,lorentey/swift,hooman/swift,benlangmuir/swift,JGiola/swift,apple/swift,jckarter/swift,JGiola/swift,stephentyrone/swift,harlanhaskins/swift,parkera/swift,shajrawi/swift,CodaFi/swift,tkremenek/swift,JGiola/swift,glessard/swift,karwa/swift,jckarter/swift,stephentyrone/swift,lorentey/swift,gribozavr/swift,parkera/swift,stephentyrone/swift,sschiau/swift,shahmishal/swift,sschiau/swift,xwu/swift,benlangmuir/swift,airspeedswift/swift,hooman/swift,gribozavr/swift,nathawes/swift,ahoppen/swift,shahmishal/swift,allevato/swift,ahoppen/swift,CodaFi/swift,CodaFi/swift,xedin/swift,roambotics/swift,gribozavr/swift,apple/swift,roambotics/swift,stephentyrone/swift,CodaFi/swift,airspeedswift/swift,benlangmuir/swift,gribozavr/swift,practicalswift/swift,rudkx/swift,atrick/swift,JGiola/swift,roambotics/swift,allevato/swift,allevato/swift,sschiau/swift,parkera/swift,rudkx/swift,harlanhaskins/swift,jckarter/swift,devincoughlin/swift,amraboelela/swift,airspeedswift/swift,glessard/swift,nathawes/swift,hooman/swift,shajrawi/swift,tkremenek/swift,stephentyrone/swift,xwu/swift,amraboelela/swift,allevato/swift,xedin/swift,JGiola/swift,aschwaighofer/swift,lorentey/swift,atrick/swift,amraboelela/swift,devincoughlin/swift,karwa/swift,karwa/swift,shajrawi/swift,practicalswift/swift,roambotics/swift,nathawes/swift,parkera/swift,practicalswift/swift,aschwaighofer/swift,practicalswift/swift,xwu/swift,shahmishal/swift,glessard/swift,ahoppen/swift,jmgc/swift,practicalswift/swift,parkera/swift,harlanhaskins/swift,gribozavr/swift,xwu/swift,xwu/swift,karwa/swift,apple/swift,CodaFi/swift,amraboelela/swift,lorentey/swift,shajrawi/swift,benlangmuir/swift,hooman/swift,roambotics/swift,shajrawi/swift,xwu/swift,JGiola/swift,nathawes/swift,jmgc/swift,jmgc/swift,CodaFi/swift,airspeedswift/swift,sschiau/swift,harlanhaskins/swift,shahmishal/swift,lorentey/swift,tkremenek/swift,devincoughlin/swift,benlangmuir/swift,jckarter/swift,rudkx/swift,xedin/swift,aschwaighofer/swift,karwa/swift,gregomni/swift,aschwaighofer/swift,lorentey/swift,atrick/swift,rudkx/swift,sschiau/swift,lorentey/swift,jmgc/swift,shajrawi/swift,gregomni/swift,aschwaighofer/swift,devincoughlin/swift,ahoppen/swift,ahoppen/swift,sschiau/swift,jmgc/swift,gribozavr/swift,aschwaighofer/swift,shahmishal/swift,glessard/swift,jckarter/swift,aschwaighofer/swift,atrick/swift,xedin/swift,jckarter/swift,shajrawi/swift,allevato/swift,hooman/swift,apple/swift,shahmishal/swift,roambotics/swift,karwa/swift,amraboelela/swift,rudkx/swift,apple/swift,tkremenek/swift,apple/swift,harlanhaskins/swift,tkremenek/swift,karwa/swift,amraboelela/swift,devincoughlin/swift,allevato/swift,nathawes/swift,stephentyrone/swift,karwa/swift,xwu/swift,jmgc/swift,harlanhaskins/swift,allevato/swift,xedin/swift,tkremenek/swift,jckarter/swift,gregomni/swift,sschiau/swift,gribozavr/swift,amraboelela/swift