CONFIG_SERIAL_CONSOLE is not available for thedefaultarchitecture x86.
Result is shown for architecture m68k

Support for serial port console


Linux Kernel Configuration
└─>Character devices
└─>Support for serial port console
In linux kernel since version 2.6.12  
If you say Y here, it will be possible to use a serial port as the
system console (the system console is the device which receives all
kernel messages and warnings and which allows logins in single user
mode). This could be useful if some terminal or printer is connected
to that serial port.

Even if you say Y here, the currently visible virtual console
(/dev/tty0) will still be used as the system console by default, but
you can alter that using a kernel command line option such as
"console=ttyS1". (Try "man bootparam" or see the documentation of
your boot loader about how to pass options to the kernel at boot

If you don't have a graphical console and you say Y here, the
kernel will automatically use the first serial line, /dev/ttyS0, as
system console.

If unsure, say N.