fix missing include in posix_madvise.c (compile error)

src/mman/posix_madvise.c

@@ -1,5 +1,6 @@
 #define _GNU_SOURCE
 #include <sys/mman.h>
+#include "syscall.h"
 
 int posix_madvise(void *addr, size_t len, int advice)
 {