[Clang importer] Compute requirement signature before setting environment.
[Clang importer] Compute requirement signature before setting environment.

Match what the type checker is doing.

jopamer/swift,OscarSwanros/swift,benlangmuir/swift,sschiau/swift,austinzheng/swift,gribozavr/swift,stephentyrone/swift,tkremenek/swift,felix91gr/swift,allevato/swift,amraboelela/swift,CodaFi/swift,djwbrown/swift,deyton/swift,apple/swift,sschiau/swift,allevato/swift,hooman/swift,tjw/swift,airspeedswift/swift,tjw/swift,practicalswift/swift,ahoppen/swift,lorentey/swift,danielmartin/swift,tkremenek/swift,allevato/swift,aschwaighofer/swift,zisko/swift,zisko/swift,JGiola/swift,uasys/swift,tjw/swift,lorentey/swift,tkremenek/swift,CodaFi/swift,glessard/swift,karwa/swift,benlangmuir/swift,danielmartin/swift,frootloops/swift,harlanhaskins/swift,danielmartin/swift,airspeedswift/swift,CodaFi/swift,jmgc/swift,austinzheng/swift,natecook1000/swift,gregomni/swift,tkremenek/swift,shahmishal/swift,practicalswift/swift,deyton/swift,jmgc/swift,alblue/swift,frootloops/swift,glessard/swift,xwu/swift,parkera/swift,gribozavr/swift,atrick/swift,nathawes/swift,tkremenek/swift,shahmishal/swift,milseman/swift,harlanhaskins/swift,jopamer/swift,devincoughlin/swift,devincoughlin/swift,aschwaighofer/swift,devincoughlin/swift,practicalswift/swift,xedin/swift,huonw/swift,xwu/swift,harlanhaskins/swift,jmgc/swift,jmgc/swift,shajrawi/swift,harlanhaskins/swift,alblue/swift,apple/swift,huonw/swift,return/swift,tjw/swift,gribozavr/swift,amraboelela/swift,brentdax/swift,jckarter/swift,devincoughlin/swift,alblue/swift,amraboelela/swift,gribozavr/swift,sschiau/swift,ahoppen/swift,atrick/swift,practicalswift/swift,natecook1000/swift,parkera/swift,milseman/swift,sschiau/swift,jckarter/swift,austinzheng/swift,apple/swift,gregomni/swift,practicalswift/swift,djwbrown/swift,allevato/swift,parkera/swift,return/swift,roambotics/swift,xwu/swift,gribozavr/swift,nathawes/swift,gregomni/swift,allevato/swift,tkremenek/swift,jckarter/swift,alblue/swift,brentdax/swift,tjw/swift,milseman/swift,felix91gr/swift,stephentyrone/swift,karwa/swift,harlanhaskins/swift,xwu/swift,OscarSwanros/swift,karwa/swift,benlangmuir/swift,djwbrown/swift,natecook1000/swift,zisko/swift,devincoughlin/swift,uasys/swift,jopamer/swift,hooman/swift,jopamer/swift,shahmishal/swift,huonw/swift,shajrawi/swift,airspeedswift/swift,parkera/swift,atrick/swift,karwa/swift,harlanhaskins/swift,shahmishal/swift,aschwaighofer/swift,danielmartin/swift,airspeedswift/swift,danielmartin/swift,CodaFi/swift,felix91gr/swift,rudkx/swift,atrick/swift,swiftix/swift,jckarter/swift,apple/swift,xwu/swift,tkremenek/swift,zisko/swift,gregomni/swift,natecook1000/swift,austinzheng/swift,xwu/swift,swiftix/swift,rudkx/swift,jopamer/swift,deyton/swift,swiftix/swift,benlangmuir/swift,alblue/swift,parkera/swift,nathawes/swift,milseman/swift,shahmishal/swift,karwa/swift,alblue/swift,apple/swift,felix91gr/swift,milseman/swift,CodaFi/swift,karwa/swift,nathawes/swift,stephentyrone/swift,hooman/swift,swiftix/swift,jckarter/swift,shajrawi/swift,xedin/swift,brentdax/swift,devincoughlin/swift,swiftix/swift,nathawes/swift,natecook1000/swift,rudkx/swift,parkera/swift,aschwaighofer/swift,shahmishal/swift,brentdax/swift,ahoppen/swift,danielmartin/swift,zisko/swift,ahoppen/swift,lorentey/swift,frootloops/swift,OscarSwanros/swift,frootloops/swift,jmgc/swift,benlangmuir/swift,sschiau/swift,OscarSwanros/swift,zisko/swift,uasys/swift,roambotics/swift,uasys/swift,stephentyrone/swift,gribozavr/swift,milseman/swift,huonw/swift,jckarter/swift,djwbrown/swift,return/swift,sschiau/swift,devincoughlin/swift,jckarter/swift,roambotics/swift,OscarSwanros/swift,gribozavr/swift,natecook1000/swift,devincoughlin/swift,swiftix/swift,aschwaighofer/swift,lorentey/swift,JGiola/swift,hooman/swift,glessard/swift,huonw/swift,sschiau/swift,uasys/swift,lorentey/swift,austinzheng/swift,CodaFi/swift,tjw/swift,huonw/swift,hooman/swift,shajrawi/swift,deyton/swift,milseman/swift,frootloops/swift,karwa/swift,lorentey/swift,shajrawi/swift,amraboelela/swift,practicalswift/swift,harlanhaskins/swift,hooman/swift,shajrawi/swift,felix91gr/swift,jmgc/swift,gribozavr/swift,xedin/swift,austinzheng/swift,allevato/swift,atrick/swift,nathawes/swift,alblue/swift,jmgc/swift,allevato/swift,rudkx/swift,stephentyrone/swift,airspeedswift/swift,xedin/swift,tjw/swift,huonw/swift,austinzheng/swift,jopamer/swift,swiftix/swift,CodaFi/swift,amraboelela/swift,felix91gr/swift,jopamer/swift,shahmishal/swift,return/swift,xedin/swift,return/swift,apple/swift,roambotics/swift,shahmishal/swift,glessard/swift,rudkx/swift,deyton/swift,roambotics/swift,frootloops/swift,OscarSwanros/swift,airspeedswift/swift,roambotics/swift,glessard/swift,parkera/swift,natecook1000/swift,frootloops/swift,danielmartin/swift,JGiola/swift,uasys/swift,return/swift,stephentyrone/swift,aschwaighofer/swift,xedin/swift,brentdax/swift,xedin/swift,stephentyrone/swift,return/swift,aschwaighofer/swift,rudkx/swift,xwu/swift,felix91gr/swift,djwbrown/swift,karwa/swift,hooman/swift,JGiola/swift,nathawes/swift,djwbrown/swift,gregomni/swift,gregomni/swift,amraboelela/swift,JGiola/swift,uasys/swift,amraboelela/swift,atrick/swift,JGiola/swift,ahoppen/swift,glessard/swift,zisko/swift,lorentey/swift,practicalswift/swift,benlangmuir/swift,brentdax/swift,ahoppen/swift,lorentey/swift,OscarSwanros/swift,djwbrown/swift,airspeedswift/swift,sschiau/swift,shajrawi/swift,xedin/swift,parkera/swift,deyton/swift,brentdax/swift,deyton/swift,practicalswift/swift,shajrawi/swift