src/libutil/util.hh: fix build on gcc-11
src/libutil/util.hh: fix build on gcc-11

Due to missing <atomic> declaration the build fails as:

    src/libutil/util.hh:350:24: error: no match for 'operator||' (operand types are 'std::atomic<bool>' and 'bool')
      350 |     if (_isInterrupted || (interruptCheck && interruptCheck()))
          |         ~~~~~~~~~~~~~~ ^~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          |         |                                 |
          |         std::atomic<bool>                 bool

NixOS/nix,rycee/nix,rycee/nix,rycee/nix,NixOS/nix,rycee/nix,NixOS/nix,NixOS/nix,rycee/nix,NixOS/nix