[PATCH] fix missing forward declaration of memset in sched.h

["Jörg Krause" <joerg.krause@embedded.rocks>]

Fixes build issue when using the macro `CPU_EQUAL()`, e.g. in Boost [1]:

```
libs/fiber/src/numa/linux/pin_thread.cpp:31:5: error: 'memset' was not declared in this scope
     CPU_ZERO( & set);
     ^
```

[1] https://github.com/boostorg/fiber/pull/142

Reported-by: Oliver Kowalke <oliver.kowalke@gmail.com>
Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
---
 include/sched.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/sched.h b/include/sched.h
index d1cccb70..05d40b1e 100644
--- a/include/sched.h
+++ b/include/sched.h
@@ -72,6 +72,7 @@ int setns(int, int);
 
 void *memcpy(void *__restrict, const void *__restrict, size_t);
 int memcmp(const void *, const void *, size_t);
+void *memset (void *, int, size_t);
 void *calloc(size_t, size_t);
 void free(void *);
 
-- 
2.14.1