Adding `@usableFromInline` to needed API
Adding `@usableFromInline` to needed API

getMainExecutor and asyncMainDrainQueue function declarations are needed
to compile programs with the asyn-main function. The functions are
declared internal, so they don't show up in the swift interface files.

JGiola/swift,apple/swift,apple/swift,glessard/swift,JGiola/swift,atrick/swift,roambotics/swift,benlangmuir/swift,gregomni/swift,JGiola/swift,rudkx/swift,apple/swift,JGiola/swift,rudkx/swift,gregomni/swift,roambotics/swift,apple/swift,atrick/swift,benlangmuir/swift,ahoppen/swift,gregomni/swift,apple/swift,ahoppen/swift,apple/swift,glessard/swift,JGiola/swift,ahoppen/swift,glessard/swift,rudkx/swift,atrick/swift,benlangmuir/swift,ahoppen/swift,benlangmuir/swift,benlangmuir/swift,glessard/swift,roambotics/swift,atrick/swift,roambotics/swift,atrick/swift,glessard/swift,rudkx/swift,benlangmuir/swift,roambotics/swift,glessard/swift,gregomni/swift,gregomni/swift,gregomni/swift,ahoppen/swift,rudkx/swift,atrick/swift,ahoppen/swift,rudkx/swift,JGiola/swift,roambotics/swift