needs features.h

libc/sysdeps/linux/x86_64/clone.S

@@ -19,6 +19,7 @@
 /* clone() is even more special than fork() as it mucks with stacks
    and invokes a function in the right context after its all over.  */
 
+#include <features.h>
 #define _ERRNO_H 1
 #include <bits/errno.h>
 #include <sys/syscall.h>