[ClangImporter] Pass -mcx16 to Clang invocation for x86_64 Linux targets
[ClangImporter] Pass -mcx16 to Clang invocation for x86_64 Linux targets

The Swift runtime and the concurrency module both use -mcx16, so there seems to be little point in not enabling it for Swift code in general.

This allows packages like swift-atomics to rely on double wide atomics always being available.

https://bugs.swift.org/browse/SR-13781

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