When linking without -O option on Cygwin, libswiftSwiftOnoneSupport.dll.a is not automatically linked. ( ./swiftc -O Hello.swift is working. )
$ ./swiftc Hello.swift
/tmp/Hello-f99214.o:(.text+0x5f): undefined reference to `_TTSg5P____TFs27_allocateUninitializedArrayurFBwTGSax_Bp_'
collect2: error: ld returned 1 exit status
clang-3.7: error: linker (via gcc) command failed with exit code 1 (use -v to see invocation)
<unknown>:0: error: link command failed with exit code 1 (use -v to see invocation)
The auto link information is well stored to the compiled object file on Cygwin. But swift-autolink-extraction is not worked for COFF.