Removed Win32 ifdef completely for sys/uio.h.
Removed Win32 ifdef completely for sys/uio.h.

No idea why we had this ifdef at all but MSVC, MingW32, Watcom
and Borland all have no sys/uio.h header; so if there's another
Win32 compiler which needs it then it should be added explicitely
instead of this negative list.

libssh2/libssh2,libssh2/libssh2,libssh2/libssh2,libssh2/libssh2