fix: preserve GCC __attribute__ between enum keyword and name in AST

[strimo378]

__attribute__ placed between enum and the tag name (e.g. enum __attribute__((packed)) color { ... }) was silently dropped from the AST. The parser consumed the tokens correctly but discarded the returned attribute list instead of attaching it to the IASTEnumerationSpecifier.

// Previously: attribute was consumed but not added to the AST node
enum __attribute__ ((packed)) color {
    RED = 1,
    GREEN = 2
};