include in both ecpg and C++

I have a header file that gets included by both C/C++ code and ecpg code.
In this header are a few structs that get used by both code (C/C++ and
ecpg). In order to get this to work for Informix, we had to do something
like this in the header file:

#ifdef TFLG
EXEC SQL BEGIN DECLARE SECTION
#endif

struct definitions

#ifdef TFLG
EXEC SQL END DECLARE SECTION
#endif

I use the EXEC SQL INCLUDE headerfile statement in my ecpg code, but of
course, not the C/C++ code.

I believe the TFLG macro gets defined by the Informix precompiler (though I
have not been able to verify this). I also have not been able to find any
sort of PostGres counterpart.

I am using the Informix compatibility switch when compiling ecpg, but do not
get a successful compile (with a number of compile variations attempted).
Does anyone know how to implement such a design? Is there a PostGres macro
that is basically the same thing or is there another method I may be able to
use?

Thanks,

Tom