configure.ac: only use Windows I/O manager on native Windows
Cygwin and MSYS2 are UNIX-compatible platforms on top of Windows, so
they should use the UNIX I/O manager, not the Windows I/O manager.
(Note that "cygwin" was misspelled as "cigwin", so the code did not have
the intended effect anyway.)
Fixes: d1d44c146a5e ("ext2fs: compile the io implementation according to os") Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>