CONFIG_WARN_STACK is not available for thedefaultarchitecture x86.
Result is shown for architecture s390
default or selected kernelversion does not have config value CONFIG_WARN_STACK.
Result is shown for kernelversion 5.4.69

Emit compiler warnings for function with broken stack usage

configname: CONFIG_WARN_STACK

Linux Kernel Configuration
└─>Base setup
└─>Emit compiler warnings for function with broken stack usage
In linux kernel since version 2.6.12  
This option enables the compiler options -mwarn-framesize and
-mwarn-dynamicstack. If the compiler supports these options it
will generate warnings for function which either use alloca or
create a stack frame bigger than CONFIG_WARN_STACK_SIZE.

Say N if you are unsure.