message: core: use existing filesystem include
  This is required for GCC 7 compatibility.
diff: #include <stdio.h>
  #include "fs.h"
  +#include "filesystem_include.h"
  #include "log.h"
  #ifndef PATH_MAX
  #define PATH_MAX 4096
  #endif
  -#include <filesystem>
  #include <random>
  namespace mavsdk {
  @@ -132,7 +132,7 @@ bool fs_rename(const std::string& old_name, const std::string& new_name)
  // Inspired by https://stackoverflow.com/a/58454949/8548472
  std::optional<std::string> create_tmp_directory(const std::string& prefix)
  {
  - const auto tmp_dir = std::filesystem::temp_directory_path();
  + const auto tmp_dir = fs::temp_directory_path();
  std::random_device dev;
  std::mt19937 prng(dev());
  @@ -145,7 +145,7 @@ std::optional<std::string> create_tmp_directory(const std::string& prefix)
  ss << prefix << '-' << std::hex << rand(prng);
  auto path = tmp_dir / ss.str();
  - const auto created = std::filesystem::create_directory(path);
  + const auto created = fs::create_directory(path);
  if (created) {
  return {path};
  }
  