Защо е с подчертавки самото "packed" ? И защо правилната версия е закоментирана?

Не може да не работи, нещо има гнило, това си е крайъгълен камък....

Target Hook: bool TARGET_MS_BITFIELD_LAYOUT_P (const_tree record_type)

This target hook returns true if bit-fields in the given record_type are to be laid out following the rules of Microsoft Visual C/C++, namely:

(i) a bit-field won't share the same storage unit with the previous bit-field if their underlying types have different sizes, and the bit-field will be aligned to the highest alignment of the underlying types of itself and of the previous bit-field; (ii) a zero-sized bit-field will affect the alignment of the whole enclosing structure, even if it is unnamed; except that (iii) a zero-sized bit-field will be disregarded unless it follows another bit-field of nonzero size. If this hook returns true, other macros that control bit-field layout are ignored.

When a bit-field is inserted into a packed record, the whole size of the underlying type is used by one or more same-size adjacent bit-fields (that is, if its long:3, 32 bits is used in the record, and any additional adjacent long bit-fields are packed into the same chunk of 32 bits. However, if the size changes, a new field of that size is allocated). In an unpacked record, this is the same as using alignment, but not equivalent when packing.

If both MS bit-fields and ‘__attribute__((packed))’ are used, the latter will take precedence. If ‘__attribute__((packed))’ is used on a single field when MS bit-fields are in use, it will take precedence for that field, but the alignment of the rest of the structure may affect its placement.