if __NR_swapon does not exist, dont try and create a syscall for it

libc/sysdeps/linux/common/swapon.c

@@ -8,5 +8,10 @@
  */
 
 #include "syscalls.h"
+
+#ifdef __NR_swapon
+
 #include <sys/swap.h>
 _syscall2(int, swapon, const char *, path, int, swapflags);
+
+#endif