[Bug c/117689] enum with underying type "extension" to GNU 17 is not documented

[sandra at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117689

--- Comment #2 from sandra at gcc dot gnu.org ---
More specifically, gcc accepts

enum e;
static enum e thing;
enum e { e1, e2, e3};

but rejects

enum e;
int foo (void)
{
  static enum e thing;
  return -1;
}
enum e { e1, e2, e3};

and also rejects

int foo (void)
{
  enum e;
  static enum e thing;
  enum e { e1, e2, e3};
  return -1;
}