[Issue 24215] New: std.traits.isBasicType!Enum returns true

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24215

          Issue ID: 24215
           Summary: std.traits.isBasicType!Enum returns true
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: snarwin+bugzilla at gmail.com

As of DMD+Phobos 2.105.2, the following program fails to compile:

---
import std.traits;
enum E { a }
static assert(!isBasicType!E);
---

According to the language spec [1], the basic types consist of `void`, `bool`,
the built-in integer types, the built-in floating-point types, and the built-in
character types. Enum types are not included.

std.traits.isBasicType should follow with the language spec, and return `false`
for enum types.

[1] https://dlang.org/spec/type.html#basic-data-types

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