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.