message: remove support for gcc 8
  we need to move to gcc 10 soonish anyway to use C++20
diff: #include "llvm/Passes/PassPlugin.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/raw_ostream.h"
  +#include <filesystem>
  #include <fstream>
  #include <iostream>
  #include <random>
  #include <unordered_map>
  #include <utility>
  -#if (__GNUC__ < 8) && (!__APPLE__)
  -# include <experimental/filesystem>
  - namespace fs = std::experimental::filesystem;
  -#else
  -# include <filesystem>
  - namespace fs = std::filesystem;
  -#endif
  -
  using namespace IR;
  using namespace llvm_util;
  using namespace tools;
  using namespace util;
  using namespace std;
  +namespace fs = std::filesystem;
  namespace {
  