message: Use RANGES_DIAGNOSTIC_IGNORE_UNNEEDED_MEMBER in scope_exit.cpp
  Fixes Clang/C2 (which has this warning and doesn't define __GNUC__) compiles.
diff: #include "../simple_test.hpp"
  #include "../test_utils.hpp"
  -#ifdef __GNUC__
  -RANGES_DIAGNOSTIC_IGNORE_PRAGMAS
  -#pragma GCC diagnostic ignored "-Wunneeded-member-function"
  -#endif
  +RANGES_DIAGNOSTIC_IGNORE_UNNEEDED_MEMBER
  namespace
  {
  