message: json: Re-apply the GCC 4.9 -> 4.8 patch
diff: @@ -123,7 +123,7 @@ using json = basic_json<>;
  #error "unsupported Clang version - see https://github.com/nlohmann/json#supported-compilers"
  #endif
  #elif defined(__GNUC__) && !(defined(__ICC) || defined(__INTEL_COMPILER))
  - #if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) < 40900
  + #if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) < 40800
  #error "unsupported GCC version - see https://github.com/nlohmann/json#supported-compilers"
  #endif
  #endif
  