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

libc/sysdeps/linux/common/swapoff.c

@@ -8,5 +8,10 @@
  */
 
 #include "syscalls.h"
+
+#ifdef __NR_swapoff
+
 #include <sys/swap.h>
 _syscall1(int, swapoff, const char *, path);
+
+#endif