post_processing do not work well in clang compiler

[zizhiyoumu-fuzz]

While I use post_processing to generate struct, I found that some structions in preprecessed do not expend.
For example,:
struct xxx;
struct statement in xxx.h,
but it's definition is in other file zzz.c,
while using struct xxx in yyy.c(#include<xxx.h>),
I found in yyy.preprocessed struct xxx is not expended, it is also
struct xxx;
This may lead to
<DataModel byte_size="0" name="xxx" type="struct"/>,
the struction is bad.
How can I to deal with the problem?