[AST] Check the signature of a nominal type before forming a conformance.
[AST] Check the signature of a nominal type before forming a conformance.

The introduction of the request-evaluator is causing some conformances
to be formed before the nominal type's signature is being checked,
causing a crash while type-checking the standard library. Ensure that this
cannot happen.

hooman/swift,shajrawi/swift,CodaFi/swift,stephentyrone/swift,harlanhaskins/swift,nathawes/swift,amraboelela/swift,danielmartin/swift,alblue/swift,xwu/swift,xwu/swift,jckarter/swift,jopamer/swift,gregomni/swift,karwa/swift,allevato/swift,harlanhaskins/swift,CodaFi/swift,jckarter/swift,jmgc/swift,practicalswift/swift,natecook1000/swift,roambotics/swift,atrick/swift,JGiola/swift,natecook1000/swift,aschwaighofer/swift,roambotics/swift,nathawes/swift,devincoughlin/swift,nathawes/swift,austinzheng/swift,devincoughlin/swift,karwa/swift,ahoppen/swift,parkera/swift,karwa/swift,xwu/swift,parkera/swift,rudkx/swift,lorentey/swift,CodaFi/swift,stephentyrone/swift,practicalswift/swift,xedin/swift,devincoughlin/swift,hooman/swift,austinzheng/swift,airspeedswift/swift,glessard/swift,brentdax/swift,jmgc/swift,gribozavr/swift,rudkx/swift,rudkx/swift,airspeedswift/swift,karwa/swift,devincoughlin/swift,karwa/swift,airspeedswift/swift,nathawes/swift,shajrawi/swift,glessard/swift,aschwaighofer/swift,apple/swift,stephentyrone/swift,shahmishal/swift,allevato/swift,jopamer/swift,shahmishal/swift,shahmishal/swift,allevato/swift,nathawes/swift,JGiola/swift,gribozavr/swift,roambotics/swift,practicalswift/swift,airspeedswift/swift,apple/swift,amraboelela/swift,jckarter/swift,atrick/swift,harlanhaskins/swift,natecook1000/swift,sschiau/swift,allevato/swift,atrick/swift,alblue/swift,jckarter/swift,alblue/swift,gribozavr/swift,shajrawi/swift,ahoppen/swift,natecook1000/swift,jmgc/swift,stephentyrone/swift,benlangmuir/swift,jmgc/swift,practicalswift/swift,natecook1000/swift,tkremenek/swift,JGiola/swift,parkera/swift,sschiau/swift,practicalswift/swift,lorentey/swift,apple/swift,sschiau/swift,devincoughlin/swift,airspeedswift/swift,JGiola/swift,aschwaighofer/swift,JGiola/swift,jmgc/swift,sschiau/swift,benlangmuir/swift,harlanhaskins/swift,brentdax/swift,jckarter/swift,jopamer/swift,devincoughlin/swift,shahmishal/swift,xedin/swift,ahoppen/swift,natecook1000/swift,stephentyrone/swift,apple/swift,practicalswift/swift,hooman/swift,shajrawi/swift,hooman/swift,danielmartin/swift,shajrawi/swift,aschwaighofer/swift,jopamer/swift,practicalswift/swift,amraboelela/swift,shahmishal/swift,rudkx/swift,lorentey/swift,harlanhaskins/swift,atrick/swift,shahmishal/swift,sschiau/swift,parkera/swift,aschwaighofer/swift,benlangmuir/swift,amraboelela/swift,JGiola/swift,jmgc/swift,austinzheng/swift,roambotics/swift,jckarter/swift,gregomni/swift,nathawes/swift,lorentey/swift,brentdax/swift,danielmartin/swift,tkremenek/swift,austinzheng/swift,apple/swift,alblue/swift,airspeedswift/swift,amraboelela/swift,jopamer/swift,apple/swift,benlangmuir/swift,aschwaighofer/swift,tkremenek/swift,lorentey/swift,amraboelela/swift,atrick/swift,sschiau/swift,hooman/swift,ahoppen/swift,atrick/swift,gribozavr/swift,xwu/swift,practicalswift/swift,alblue/swift,shahmishal/swift,sschiau/swift,gribozavr/swift,CodaFi/swift,xedin/swift,alblue/swift,tkremenek/swift,lorentey/swift,xedin/swift,austinzheng/swift,glessard/swift,nathawes/swift,glessard/swift,hooman/swift,gregomni/swift,rudkx/swift,rudkx/swift,danielmartin/swift,gregomni/swift,amraboelela/swift,lorentey/swift,harlanhaskins/swift,parkera/swift,brentdax/swift,benlangmuir/swift,stephentyrone/swift,brentdax/swift,lorentey/swift,xedin/swift,glessard/swift,tkremenek/swift,xwu/swift,allevato/swift,shahmishal/swift,hooman/swift,parkera/swift,devincoughlin/swift,parkera/swift,xedin/swift,jmgc/swift,roambotics/swift,ahoppen/swift,xwu/swift,benlangmuir/swift,sschiau/swift,brentdax/swift,stephentyrone/swift,danielmartin/swift,austinzheng/swift,gribozavr/swift,CodaFi/swift,tkremenek/swift,xedin/swift,allevato/swift,jopamer/swift,austinzheng/swift,CodaFi/swift,danielmartin/swift,shajrawi/swift,alblue/swift,karwa/swift,brentdax/swift,roambotics/swift,glessard/swift,gribozavr/swift,gregomni/swift,shajrawi/swift,xedin/swift,aschwaighofer/swift,harlanhaskins/swift,ahoppen/swift,tkremenek/swift,jopamer/swift,shajrawi/swift,karwa/swift,parkera/swift,danielmartin/swift,devincoughlin/swift,xwu/swift,jckarter/swift,allevato/swift,natecook1000/swift,CodaFi/swift,gregomni/swift,karwa/swift,gribozavr/swift,airspeedswift/swift