configure: Fix check for --with-login-shell on Windows

configure: Fix check for --with-login-shell on Windows

The check is supposed to stop users from trying to compile
virt-login-shell on Windows by erroring out during the
configure phase; however, there are two flaws in it:

  * the value of "x$with_win" is compared to "yes" instead
    of "xyes" (note the "x" in the first string)

  * "test" is not being used, so the script will actually
    try to run a command called "x$with_win" instead of
    performing string comparison

This patch fixes both issues.