No warnings when redefining empty named enumerations

[Daniel-Cortez]

Issue description:

Normally the compiler warns the user when they define two enumerations with the same name:

enum test {
	elem1
};
enum test {}; // warning 201: redefinition of constant/macro (symbol "test1")

But if the first enum is empty, redefinition goes unnoticed:

enum test {};
enum test {}; // No warning(s)

Minimal complete verifiable example (MCVE):

See above.

Workspace Information:

• Compiler version: 3.2.3664, 3.10.10
• Command line arguments provided (or sampctl version):
• Operating System:

[Daniel-Cortez]

Fixed in #577.