Fixed handling of AMD64 processor architecture
Fixed handling of AMD64 processor architecture

Signed-off-by: Kim Topley <b240e9af83531ac049af314c640f722869aeb57d@apple.com>

apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch