https://issues.dlang.org/show_bug.cgi?id=23696

          Issue ID: 23696
           Summary: compilable/enumbase.c:3:8: error: expected identifier
                    or ‘(’ before ‘:’ token
           Product: D
           Version: D2
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: ibuclaw@gdcproject.org

When compiling the test with `gcc -std=c11 -fsyntax-only`

compilable/enumbase.c:3:8: error: expected identifier or ‘(’ before ‘:’ token
    3 | enum E : char { A = 3, B };
      |        ^
compilable/enumbase.c:5:23: error: invalid application of ‘sizeof’ to
incomplete type ‘enum E’
    5 | _Static_assert(sizeof(enum E) == 1, "1");
      |                       ^~~~
compilable/enumbase.c:5:16: error: expression in static assertion is not an
integer
    5 | _Static_assert(sizeof(enum E) == 1, "1");
      |                ^~~~~~
compilable/enumbase.c:6:16: error: ‘A’ undeclared here (not in a function)
    6 | _Static_assert(A == 3, "2");
      |                ^
compilable/enumbase.c:6:16: error: expression in static assertion is not an
integer
compilable/enumbase.c:11:7: error: expected identifier or ‘(’ before ‘:’ token
   11 | enum L: long long {
      |       ^
compilable/enumbase.c:15:7: error: expected identifier or ‘(’ before ‘:’ token
   15 | enum U: unsigned long long {
      |       ^
compilable/enumbase.c:19:8: error: expected identifier or ‘(’ before ‘:’ token
   19 | enum U2: unsigned {
      |        ^
compilable/enumbase.c:23:8: error: expected identifier or ‘(’ before ‘:’ token
   23 | enum U3: unsigned long {
      |        ^


Original test case:
```
// https://issues.dlang.org/show_bug.cgi?id=22631

enum E : char { A = 3, B };

_Static_assert(sizeof(enum E) == 1, "1");
_Static_assert(A == 3, "2");


// https://issues.dlang.org/show_bug.cgi?id=22705

enum L: long long {
    L_A = 1,
};

enum U: unsigned long long {
    U_A = 1,
};

enum U2: unsigned {
    U2_A = 1,
};

enum U3: unsigned long {
    U3_A = 1,
};
```

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