[Bug c++/64758] [C++11] Give better error message when name of enum's base type cannot be resolved

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64758

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It got worse (maybe better) in GCC 9.4.0 and 10+:
<source>:3:14: error: found ':' in nested-name-specifier, expected '::'
    3 |   enum Waldo : uint32_t {   // oops, forgot to include <stdint.h>
      |              ^
      |              ::
<source>:3:8: error: 'Waldo' has not been declared
    3 |   enum Waldo : uint32_t {   // oops, forgot to include <stdint.h>
      |        ^~~~~
<source>:3:25: error: expected unqualified-id before '{' token
    3 |   enum Waldo : uint32_t {   // oops, forgot to include <stdint.h>
      |                         ^