libctf: get the offsets of fields of unnamed structs/unions right

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.
4 files changed