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.

(cherry picked from commit ccf58bd7)

m4/virt-login-shell.m4

@@ -22,7 +22,7 @@ AC_DEFUN([LIBVIRT_CHECK_LOGIN_SHELL], [
 
   if test "x$with_login_shell" != "xno"; then
     if test "x$with_win" = "xyes"; then
-      if "x$with_login_shell" = "yes"; then
+      if test "x$with_login_shell" = "xyes"; then
         AC_MSG_ERROR([virt-login-shell is not supported on Windows])
       else
         with_login_shell=no;