message: elle.log: fix portability issue
diff: #include <elle/log/TextLogger.hh>
  -#include <iostream>
  #include <unistd.h>
  +#include <array>
  +//#include <iomanip> // put_time
  +#include <iostream>
  +
  #include <boost/algorithm/string/classification.hpp>
  #include <boost/algorithm/string/split.hpp>
  #include <boost/algorithm/string/trim.hpp>
  @@ -164,8 +167,15 @@ namespace elle
  auto const t = Clock::to_time_t(msg.time);
  auto const tm
  = (this->time_universal() ? std::gmtime : std::localtime)(&t);
  - auto os = std::ostringstream{};
  - os << std::put_time(tm, "%F %T");
  + auto&& os = std::ostringstream{};
  + // GCC 4.9 does not support put_time.
  + // os << std::put_time(tm, "%F %T");
  + {
  + // strlen("2017-07-31 05:24:53") = 20;
  + auto buf = std::array<char, 24>{};
  + std::strftime(buf.data(), buf.size(), "%F %T", tm);
  + os << buf.data();
  + }
  if (this->time_microsec())
  {
  auto const ms =
  