use libc htonll if found

src/tools.c

@@ -21,6 +21,7 @@
 #include "procedures.h"
 #include "tools.h"
 
+#ifndef htonll
   static uint64_t htonll (uint64_t value) {
   #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
     return ((uint64_t)htonl((uint32_t)(value >> 32))) |
@@ -29,6 +30,7 @@ static uint64_t htonll (uint64_t value) {
     return value;
   #endif
   }
+#endif
 
 // Keep track of the total amount of bytes received with recv_all
 // Helps notice misread packets and clean up after errors