Do not allow tags inside the braces of unnamed enums

[Daniel-Cortez]

What this PR does / why we need it:

This PR fixes a problem with the compiler silently ignoring tags inside the braces of unnamed enums.
Before:

enum
{
    Float:DRAW_DISTANCE = 100.0 // This code compiles, but the 'Float' tag
                                // is silently ignored and the constant is defined
                                // as "DRAW_DISTANCE = _:100.0", so if someone uses it,
                                // then instead of "100.0" they'll get "float(_:100.0)"
};

After:

enum
{
    Float:DRAW_DISTANCE = 100.0 // error 001: expected token: "-identifier-", but found "-label-"
};

Which issue(s) this PR fixes:

Fixes #444

What kind of pull this is:

• A Bug Fix
• A New Feature
• Some repository meta (documentation, etc)
• Other

Additional Documentation: