[ClangImporter] Don't bother running lookups on submodules.
[ClangImporter] Don't bother running lookups on submodules.

We're only using Clang submodules for their imports and link dependencies;
they don't contain decls right now.

Swift SVN r17520

MukeshKumarS/Swift,sschiau/swift,glessard/swift,jmgc/swift,lorentey/swift,sdulal/swift,kperryua/swift,tkremenek/swift,Jnosh/swift,tardieu/swift,therealbnut/swift,ahoppen/swift,hooman/swift,JaSpa/swift,glessard/swift,xedin/swift,ahoppen/swift,KrishMunot/swift,huonw/swift,devincoughlin/swift,uasys/swift,glessard/swift,MukeshKumarS/Swift,codestergit/swift,manavgabhawala/swift,return/swift,bitjammer/swift,devincoughlin/swift,ahoppen/swift,karwa/swift,deyton/swift,gmilos/swift,gottesmm/swift,arvedviehweger/swift,kentya6/swift,felix91gr/swift,slavapestov/swift,MukeshKumarS/Swift,swiftix/swift,Ivacker/swift,uasys/swift,emilstahl/swift,LeoShimonaka/swift,slavapestov/swift,therealbnut/swift,shahmishal/swift,MukeshKumarS/Swift,hooman/swift,frootloops/swift,alblue/swift,stephentyrone/swift,arvedviehweger/swift,tinysun212/swift-windows,sschiau/swift,sdulal/swift,modocache/swift,JGiola/swift,IngmarStein/swift,nathawes/swift,shahmishal/swift,mightydeveloper/swift,calebd/swift,frootloops/swift,milseman/swift,airspeedswift/swift,tinysun212/swift-windows,cbrentharris/swift,IngmarStein/swift,JGiola/swift,calebd/swift,kusl/swift,gmilos/swift,tjw/swift,dreamsxin/swift,brentdax/swift,apple/swift,OscarSwanros/swift,deyton/swift,KrishMunot/swift,dreamsxin/swift,return/swift,swiftix/swift.old,Jnosh/swift,harlanhaskins/swift,swiftix/swift.old,practicalswift/swift,xwu/swift,johnno1962d/swift,modocache/swift,glessard/swift,danielmartin/swift,russbishop/swift,felix91gr/swift,khizkhiz/swift,allevato/swift,slavapestov/swift,manavgabhawala/swift,russbishop/swift,IngmarStein/swift,cbrentharris/swift,alblue/swift,karwa/swift,frootloops/swift,tjw/swift,natecook1000/swift,frootloops/swift,austinzheng/swift,xedin/swift,gottesmm/swift,tkremenek/swift,zisko/swift,huonw/swift,shahmishal/swift,amraboelela/swift,ben-ng/swift,xwu/swift,devincoughlin/swift,huonw/swift,austinzheng/swift,amraboelela/swift,emilstahl/swift,benlangmuir/swift,nathawes/swift,cbrentharris/swift,xwu/swift,nathawes/swift,lorentey/swift,mightydeveloper/swift,gmilos/swift,xwu/swift,Jnosh/swift,mightydeveloper/swift,adrfer/swift,IngmarStein/swift,xwu/swift,sdulal/swift,cbrentharris/swift,sdulal/swift,tkremenek/swift,practicalswift/swift,tjw/swift,parkera/swift,tardieu/swift,swiftix/swift.old,IngmarStein/swift,jtbandes/swift,roambotics/swift,dduan/swift,xedin/swift,jckarter/swift,tinysun212/swift-windows,codestergit/swift,austinzheng/swift,jmgc/swift,airspeedswift/swift,shajrawi/swift,parkera/swift,mightydeveloper/swift,practicalswift/swift,stephentyrone/swift,practicalswift/swift,manavgabhawala/swift,russbishop/swift,hughbe/swift,amraboelela/swift,hughbe/swift,karwa/swift,KrishMunot/swift,tjw/swift,apple/swift,jopamer/swift,calebd/swift,codestergit/swift,djwbrown/swift,shahmishal/swift,ben-ng/swift,felix91gr/swift,kusl/swift,airspeedswift/swift,danielmartin/swift,deyton/swift,natecook1000/swift,khizkhiz/swift,glessard/swift,shahmishal/swift,tkremenek/swift,sschiau/swift,natecook1000/swift,slavapestov/swift,cbrentharris/swift,LeoShimonaka/swift,ken0nek/swift,SwiftAndroid/swift,kstaring/swift,jckarter/swift,roambotics/swift,alblue/swift,frootloops/swift,allevato/swift,austinzheng/swift,ken0nek/swift,SwiftAndroid/swift,adrfer/swift,gottesmm/swift,airspeedswift/swift,manavgabhawala/swift,jopamer/swift,amraboelela/swift,russbishop/swift,deyton/swift,brentdax/swift,huonw/swift,LeoShimonaka/swift,natecook1000/swift,return/swift,emilstahl/swift,jmgc/swift,johnno1962d/swift,Ivacker/swift,practicalswift/swift,aschwaighofer/swift,kentya6/swift,tkremenek/swift,ken0nek/swift,bitjammer/swift,codestergit/swift,austinzheng/swift,codestergit/swift,kstaring/swift,xedin/swift,brentdax/swift,MukeshKumarS/Swift,atrick/swift,khizkhiz/swift,bitjammer/swift,SwiftAndroid/swift,parkera/swift,gmilos/swift,jmgc/swift,austinzheng/swift,return/swift,huonw/swift,zisko/swift,milseman/swift,xwu/swift,gribozavr/swift,karwa/swift,stephentyrone/swift,kentya6/swift,shahmishal/swift,kentya6/swift,jtbandes/swift,tardieu/swift,felix91gr/swift,MukeshKumarS/Swift,gregomni/swift,KrishMunot/swift,allevato/swift,therealbnut/swift,Ivacker/swift,Jnosh/swift,OscarSwanros/swift,dduan/swift,LeoShimonaka/swift,emilstahl/swift,kentya6/swift,bitjammer/swift,ben-ng/swift,atrick/swift,practicalswift/swift,swiftix/swift,djwbrown/swift,hughbe/swift,atrick/swift,jckarter/swift,Ivacker/swift,JGiola/swift,kusl/swift,lorentey/swift,kperryua/swift,IngmarStein/swift,tinysun212/swift-windows,jtbandes/swift,SwiftAndroid/swift,gregomni/swift,harlanhaskins/swift,jtbandes/swift,shahmishal/swift,ken0nek/swift,tjw/swift,apple/swift,tinysun212/swift-windows,xedin/swift,therealbnut/swift,arvedviehweger/swift,uasys/swift,johnno1962d/swift,swiftix/swift,hooman/swift,tkremenek/swift,hughbe/swift,hooman/swift,allevato/swift,ben-ng/swift,benlangmuir/swift,hooman/swift,apple/swift,swiftix/swift.old,kstaring/swift,calebd/swift,djwbrown/swift,devincoughlin/swift,gottesmm/swift,CodaFi/swift,shajrawi/swift,xedin/swift,sdulal/swift,xwu/swift,dduan/swift,JGiola/swift,codestergit/swift,dduan/swift,gribozavr/swift,ahoppen/swift,emilstahl/swift,aschwaighofer/swift,alblue/swift,zisko/swift,harlanhaskins/swift,return/swift,KrishMunot/swift,russbishop/swift,airspeedswift/swift,brentdax/swift,practicalswift/swift,gribozavr/swift,russbishop/swift,tardieu/swift,hughbe/swift,gregomni/swift,JGiola/swift,kperryua/swift,modocache/swift,alblue/swift,jmgc/swift,Ivacker/swift,nathawes/swift,khizkhiz/swift,arvedviehweger/swift,kstaring/swift,slavapestov/swift,devincoughlin/swift,adrfer/swift,swiftix/swift.old,jopamer/swift,tjw/swift,SwiftAndroid/swift,MukeshKumarS/Swift,tinysun212/swift-windows,return/swift,brentdax/swift,gottesmm/swift,parkera/swift,djwbrown/swift,CodaFi/swift,OscarSwanros/swift,milseman/swift,glessard/swift,CodaFi/swift,hooman/swift,allevato/swift,sdulal/swift,JaSpa/swift,jtbandes/swift,JaSpa/swift,CodaFi/swift,ken0nek/swift,jckarter/swift,ben-ng/swift,JaSpa/swift,kusl/swift,tardieu/swift,jckarter/swift,uasys/swift,codestergit/swift,deyton/swift,felix91gr/swift,shajrawi/swift,johnno1962d/swift,djwbrown/swift,KrishMunot/swift,calebd/swift,slavapestov/swift,Jnosh/swift,xedin/swift,SwiftAndroid/swift,gribozavr/swift,airspeedswift/swift,emilstahl/swift,kperryua/swift,hughbe/swift,deyton/swift,gribozavr/swift,austinzheng/swift,swiftix/swift,zisko/swift,kstaring/swift,ben-ng/swift,gregomni/swift,natecook1000/swift,LeoShimonaka/swift,johnno1962d/swift,benlangmuir/swift,amraboelela/swift,khizkhiz/swift,adrfer/swift,kentya6/swift,mightydeveloper/swift,airspeedswift/swift,atrick/swift,devincoughlin/swift,roambotics/swift,Ivacker/swift,karwa/swift,Jnosh/swift,Ivacker/swift,gmilos/swift,kusl/swift,danielmartin/swift,cbrentharris/swift,felix91gr/swift,calebd/swift,OscarSwanros/swift,OscarSwanros/swift,bitjammer/swift,brentdax/swift,ahoppen/swift,shajrawi/swift,kperryua/swift,kperryua/swift,calebd/swift,stephentyrone/swift,lorentey/swift,zisko/swift,LeoShimonaka/swift,alblue/swift,parkera/swift,harlanhaskins/swift,ken0nek/swift,amraboelela/swift,swiftix/swift,jmgc/swift,alblue/swift,uasys/swift,gregomni/swift,arvedviehweger/swift,kusl/swift,nathawes/swift,milseman/swift,harlanhaskins/swift,djwbrown/swift,LeoShimonaka/swift,russbishop/swift,SwiftAndroid/swift,arvedviehweger/swift,LeoShimonaka/swift,jopamer/swift,aschwaighofer/swift,zisko/swift,ken0nek/swift,brentdax/swift,kstaring/swift,huonw/swift,CodaFi/swift,harlanhaskins/swift,swiftix/swift.old,roambotics/swift,OscarSwanros/swift,rudkx/swift,mightydeveloper/swift,JaSpa/swift,atrick/swift,kstaring/swift,apple/swift,aschwaighofer/swift,parkera/swift,practicalswift/swift,parkera/swift,danielmartin/swift,gottesmm/swift,swiftix/swift.old,benlangmuir/swift,manavgabhawala/swift,milseman/swift,therealbnut/swift,karwa/swift,ben-ng/swift,aschwaighofer/swift,OscarSwanros/swift,KrishMunot/swift,rudkx/swift,tardieu/swift,frootloops/swift,dduan/swift,shajrawi/swift,emilstahl/swift,modocache/swift,johnno1962d/swift,Ivacker/swift,harlanhaskins/swift,Jnosh/swift,djwbrown/swift,natecook1000/swift,gottesmm/swift,atrick/swift,mightydeveloper/swift,kusl/swift,karwa/swift,gribozavr/swift,cbrentharris/swift,milseman/swift,lorentey/swift,khizkhiz/swift,aschwaighofer/swift,huonw/swift,swiftix/swift,ahoppen/swift,stephentyrone/swift,adrfer/swift,JaSpa/swift,uasys/swift,therealbnut/swift,CodaFi/swift,shajrawi/swift,uasys/swift,emilstahl/swift,gmilos/swift,jopamer/swift,danielmartin/swift,manavgabhawala/swift,amraboelela/swift,shahmishal/swift,aschwaighofer/swift,deyton/swift,tjw/swift,shajrawi/swift,CodaFi/swift,johnno1962d/swift,arvedviehweger/swift,allevato/swift,rudkx/swift,frootloops/swift,jtbandes/swift,sschiau/swift,return/swift,sschiau/swift,lorentey/swift,IngmarStein/swift,danielmartin/swift,manavgabhawala/swift,parkera/swift,sschiau/swift,therealbnut/swift,milseman/swift,stephentyrone/swift,shajrawi/swift,allevato/swift,zisko/swift,devincoughlin/swift,nathawes/swift,benlangmuir/swift,gribozavr/swift,tinysun212/swift-windows,sschiau/swift,hooman/swift,jmgc/swift,lorentey/swift,JaSpa/swift,bitjammer/swift,kentya6/swift,tardieu/swift,devincoughlin/swift,kperryua/swift,kusl/swift,swiftix/swift,adrfer/swift,jopamer/swift,dduan/swift,jtbandes/swift,modocache/swift,felix91gr/swift,sschiau/swift,gmilos/swift,dduan/swift,nathawes/swift,bitjammer/swift,natecook1000/swift,jckarter/swift,roambotics/swift,khizkhiz/swift,slavapestov/swift,karwa/swift,adrfer/swift,rudkx/swift,mightydeveloper/swift,swiftix/swift.old,JGiola/swift,kentya6/swift,modocache/swift,sdulal/swift,danielmartin/swift,stephentyrone/swift,xedin/swift,hughbe/swift,gribozavr/swift,tkremenek/swift,modocache/swift,sdulal/swift,apple/swift,rudkx/swift,jopamer/swift,lorentey/swift,rudkx/swift,benlangmuir/swift,jckarter/swift,cbrentharris/swift,gregomni/swift,roambotics/swift