implement stub versions of sched_*

these actually work, but for now they prohibit actually setting
priority levels and report min/max priority as 0.

src/sched/sched_get_priority_max.c

+#include <sched.h>
+
+int sched_get_priority_max(int policy)
+{
+	return 0;
+}
+
+int sched_get_priority_min(int policy)
+{
+	return 0;
+}

src/sched/sched_getparam.c

+#include <sched.h>
+#include "syscall.h"
+
+int sched_getparam(pid_t pid, struct sched_param *param)
+{
+	return syscall(SYS_sched_getparam, pid, param);
+}

src/sched/sched_getscheduler.c

+#include <sched.h>
+#include "syscall.h"
+
+int sched_getscheduler(pid_t pid)
+{
+	return syscall(SYS_sched_getscheduler, pid);
+}

src/sched/sched_rr_get_interval.c

+#include <sched.h>
+#include "syscall.h"
+
+int sched_rr_get_interval(pid_t pid, struct timespec *ts)
+{
+	return syscall(SYS_sched_rr_get_interval, pid, ts);
+}
+

src/sched/sched_setparam.c

+#include <sched.h>
+#include "syscall.h"
+
+int sched_setparam(pid_t pid, const struct sched_param *param)
+{
+	static const struct sched_param def;
+	return syscall(SYS_sched_setparam, pid, &def);
+}

src/sched/sched_setscheduler.c

+#include <sched.h>
+#include "syscall.h"
+
+int sched_setscheduler(pid_t pid, int sched, const struct sched_param *param)
+{
+	static const struct sched_param def;
+	return syscall(SYS_sched_setscheduler, pid, sched, &def);
+}