query: __attribute__ in gcc vs g++

[Chris Dollin]

The following fragment:

    #define __stdcall __attribute__((__stdcall__))
    #define CALLBACK    __stdcall

    typedef int (CALLBACK *foo)( int );

compiles silently using gcc but not using g++ (which issues
error messages as if it were December 31st).
(--version says "egcs-2.91.66" for both).

[this comes from trying to use the Wine header files for
porting a Windows program written in C++.]

What obvious thing am I doing wrong?

-- 
Chris "baffled by featurelessness" Dollin