sched.h: Add SCHED_DEADLINE

Defined in kernel v3.14, commit
aab03e05e8f7 ("sched/deadline: Add SCHED_DEADLINE structures & implementation")

Signed-off-by: Petr Vorel <petr.vorel@gmail.com>

libc/sysdeps/linux/common/bits/sched.h

@@ -31,6 +31,7 @@
 #ifdef __USE_GNU
 # define SCHED_BATCH		3
 # define SCHED_IDLE		5
+# define SCHED_DEADLINE	6
 
 # define SCHED_RESET_ON_FORK	0x40000000
 #endif