This feature is referred to as "code/data literals" in ASMotor,
and simply as "literals" in some older assemblers like MIDAS
for the PDP-10. RGBASM already had the "section fragments"
feature for keeping disparate contents together when linked,
so these worked naturally as "fragment literals".
This message is only printed for identifiers parsed as
`T_LABEL` (since they're at the start of a line) but
already defined as macros. Otherwise it may not be
relevant, e.g. for `MyLabel;:` or `My Label::`.
