CONFIG_DEBUG_UART_8250_FLOW_CONTROL is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

Enable flow control for 8250 UART

configname: CONFIG_DEBUG_UART_8250_FLOW_CONTROL

Linux Kernel Configuration
└─>Enable flow control for 8250 UART
In linux kernel since version 3.12 (release Date: 2013-11-03)