[stdlib/cygwin] Add sys/file.h for compatibility.
[stdlib/cygwin] Add sys/file.h for compatibility.

sys/file.h defines L_SET, L_INCR, etc. They are used in Foundation.

tinysun212/swift-windows,tinysun212/swift-windows,tinysun212/swift-windows,tinysun212/swift-windows,tinysun212/swift-windows,tinysun212/swift-windows,tinysun212/swift-windows