building ntdll on cygwin

[Steven Edwards]

we get much futher now when building ntdll on cygwin. when linking I am 
getting the following error

ntdll.exp(.edata+0xe4c):fake: undefined reference to `NTDLL_alloca_probe@0'
ntdll.exp(.edata+0xe5c):fake: undefined reference to `NTDLL_chkstk@0'

there are some other warnings but this is the only major thing with ntdll.

Thanks
Steven