[Test] Disable Prototypes/BigInt.swift.
[Test] Disable Prototypes/BigInt.swift.

While baking a solution that works for both Windows and other platforms,
disable the test.

Most recent failure is here

https://ci.swift.org/view/Dashboard/job/oss-swift_tools-R_stdlib-RD_test-simulator/5173/consoleText

rdar://problem/65251059

jckarter/swift,JGiola/swift,jmgc/swift,airspeedswift/swift,JGiola/swift,atrick/swift,parkera/swift,tkremenek/swift,nathawes/swift,ahoppen/swift,airspeedswift/swift,gregomni/swift,jmgc/swift,hooman/swift,jckarter/swift,CodaFi/swift,rudkx/swift,CodaFi/swift,jckarter/swift,apple/swift,atrick/swift,xwu/swift,airspeedswift/swift,jmgc/swift,allevato/swift,jckarter/swift,xwu/swift,benlangmuir/swift,apple/swift,allevato/swift,ahoppen/swift,atrick/swift,benlangmuir/swift,roambotics/swift,gregomni/swift,jmgc/swift,glessard/swift,xwu/swift,parkera/swift,allevato/swift,allevato/swift,roambotics/swift,JGiola/swift,JGiola/swift,ahoppen/swift,nathawes/swift,apple/swift,rudkx/swift,atrick/swift,nathawes/swift,apple/swift,parkera/swift,parkera/swift,CodaFi/swift,tkremenek/swift,hooman/swift,benlangmuir/swift,glessard/swift,ahoppen/swift,apple/swift,roambotics/swift,xwu/swift,airspeedswift/swift,CodaFi/swift,parkera/swift,roambotics/swift,gregomni/swift,hooman/swift,airspeedswift/swift,hooman/swift,rudkx/swift,benlangmuir/swift,jckarter/swift,hooman/swift,parkera/swift,atrick/swift,parkera/swift,atrick/swift,roambotics/swift,allevato/swift,tkremenek/swift,jmgc/swift,ahoppen/swift,hooman/swift,gregomni/swift,airspeedswift/swift,apple/swift,allevato/swift,CodaFi/swift,rudkx/swift,benlangmuir/swift,jmgc/swift,glessard/swift,xwu/swift,tkremenek/swift,tkremenek/swift,glessard/swift,hooman/swift,parkera/swift,airspeedswift/swift,xwu/swift,gregomni/swift,jckarter/swift,jmgc/swift,nathawes/swift,benlangmuir/swift,JGiola/swift,glessard/swift,gregomni/swift,glessard/swift,allevato/swift,tkremenek/swift,xwu/swift,roambotics/swift,JGiola/swift,nathawes/swift,rudkx/swift,rudkx/swift,CodaFi/swift,jckarter/swift,nathawes/swift,CodaFi/swift,ahoppen/swift,nathawes/swift,tkremenek/swift