Why doesn't the GCC give any warning to these unused variables in the Linux kernel?

Normally, the compiler warns if a variable is declared but is never referenced. In the Linux kernel source code, some unused functions and variables are marked __atrribute__((unused)). ==> https://livegrep.com/search/linux?q=__attribute__((unused)) GCC, on the other hand, does not provide any warnings for these unused and unmarked variables like the integer flags in kernel/sched/idle.c#427<https://elixir.bootlin.com/linux/latest/source/kernel/sched/idle.c#L427> . Why?