add support for thread scheduling (POSIX TPS option)

linux's sched_* syscalls actually implement the TPS (thread
scheduling) functionality, not the PS (process scheduling)
functionality which the sched_* functions are supposed to have.
omitting support for the PS option (and having the sched_* interfaces
fail with ENOSYS rather than omitting them, since some broken software
assumes they exist) seems to be the only conforming way to do this on
linux.

src/sched/sched_get_priority_max.c

@@ -1,11 +1,12 @@
 #include <sched.h>
+#include "syscall.h"
 
 int sched_get_priority_max(int policy)
 {
-	return 0;
+	return syscall(SYS_sched_get_priority_max, policy);
 }
 
 int sched_get_priority_min(int policy)
 {
-	return 0;
+	return syscall(SYS_sched_get_priority_min, policy);
 }

src/sched/sched_getparam.c

@@ -1,7 +1,8 @@
 #include <sched.h>
+#include <errno.h>
 #include "syscall.h"
 
 int sched_getparam(pid_t pid, struct sched_param *param)
 {
-	return syscall(SYS_sched_getparam, pid, param);
+	return __syscall_ret(-ENOSYS);
 }

src/sched/sched_getscheduler.c

@@ -1,7 +1,8 @@
 #include <sched.h>
+#include <errno.h>
 #include "syscall.h"
 
 int sched_getscheduler(pid_t pid)
 {
-	return syscall(SYS_sched_getscheduler, pid);
+	return __syscall_ret(-ENOSYS);
 }

src/sched/sched_rr_get_interval.c

@@ -5,4 +5,3 @@ 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

@@ -1,8 +1,8 @@
 #include <sched.h>
+#include <errno.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);
+	return __syscall_ret(-ENOSYS);
 }

src/sched/sched_setscheduler.c

@@ -1,8 +1,8 @@
 #include <sched.h>
+#include <errno.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, 0, &def);
+	return __syscall_ret(-ENOSYS);
 }