We were failing to add the offsets of the containing struct/union
in this case, leading to all offsets being relative to the unnamed
struct/union itself.
libctf/
PR libctf/30264
* ctf-types.c (ctf_member_info): Add the offset of the unnamed
member of the current struct as necessary.
* testsuite/libctf-lookup/unnamed-field-info*: New test.
