GSB: More accurate recursion check in GenericSignatureBuilder::resolve()
GSB: More accurate recursion check in GenericSignatureBuilder::resolve()

I found this by inspection. isExplicit() returns false for inferred
requirements, which is probably not what we want here. Using isDerived()
seems better instead.

roambotics/swift,atrick/swift,benlangmuir/swift,roambotics/swift,apple/swift,ahoppen/swift,rudkx/swift,ahoppen/swift,glessard/swift,apple/swift,gregomni/swift,gregomni/swift,rudkx/swift,parkera/swift,parkera/swift,tkremenek/swift,benlangmuir/swift,JGiola/swift,gregomni/swift,tkremenek/swift,glessard/swift,glessard/swift,ahoppen/swift,glessard/swift,parkera/swift,gregomni/swift,hooman/swift,hooman/swift,JGiola/swift,roambotics/swift,ahoppen/swift,benlangmuir/swift,atrick/swift,tkremenek/swift,hooman/swift,rudkx/swift,parkera/swift,parkera/swift,tkremenek/swift,apple/swift,parkera/swift,tkremenek/swift,apple/swift,benlangmuir/swift,roambotics/swift,hooman/swift,tkremenek/swift,rudkx/swift,hooman/swift,roambotics/swift,xwu/swift,xwu/swift,JGiola/swift,xwu/swift,ahoppen/swift,glessard/swift,gregomni/swift,ahoppen/swift,atrick/swift,JGiola/swift,parkera/swift,JGiola/swift,xwu/swift,atrick/swift,rudkx/swift,benlangmuir/swift,hooman/swift,atrick/swift,gregomni/swift,JGiola/swift,hooman/swift,xwu/swift,xwu/swift,xwu/swift,glessard/swift,benlangmuir/swift,tkremenek/swift,roambotics/swift,rudkx/swift,apple/swift,apple/swift,parkera/swift,atrick/swift