sched: Clean up and standardize #if/#else/#endif markers in sched/syscalls.c

- Use the standard #ifdef marker format for larger blocks,
   where appropriate:

        #if CONFIG_FOO
        ...
        #else /* !CONFIG_FOO: */
        ...
        #endif /* !CONFIG_FOO */

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20250528080924.2273858-18-mingo@kernel.org

kernel/sched/syscalls.c

@@ -174,7 +174,7 @@ SYSCALL_DEFINE1(nice, int, increment)
 	return 0;
 }
 
-#endif
+#endif /* __ARCH_WANT_SYS_NICE */
 
 /**
  * task_prio - return the priority value of a given task.
@@ -255,8 +255,7 @@ int sched_core_idle_cpu(int cpu)
 
 	return idle_cpu(cpu);
 }
-
-#endif
+#endif /* CONFIG_SCHED_CORE */
 
 /**
  * find_process_by_pid - find a process with a matching PID value.
@@ -448,7 +447,7 @@ static inline int uclamp_validate(struct task_struct *p,
 }
 static void __setscheduler_uclamp(struct task_struct *p,
 				  const struct sched_attr *attr) { }
-#endif
+#endif /* !CONFIG_UCLAMP_TASK */
 
 /*
  * Allow unprivileged RT tasks to decrease priority.
@@ -658,7 +657,7 @@ int __sched_setscheduler(struct task_struct *p,
 				goto unlock;
 			}
 		}
-#endif
+#endif /* CONFIG_SMP */
 	}
 
 	/* Re-check policy now with rq lock held: */