[AST] NFC: Add reentrancy check to associated type anchor walk
[AST] NFC: Add reentrancy check to associated type anchor walk

This makes compiler crasher 28870 crash faster and reliably instead of
recursing off the end of the stack.

This reverts: 614cb48b63f29325e5b7aee267602c2c27f1a3c6

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