in-expression compile-time check for constant expressions for older G++

Question

I have the following macros for certain compile-time checks:

/* in-expression compile-time check evaluating to 0 */
#ifdef __cplusplus
template<bool> struct Chk_sa;
template<> struct Chk_sa<true>{};
#define Chk(test) (sizeof((Chk_sa<!!(0+(test))>())) * 0)
#else
#define Chk(test) (sizeof(struct { int (Chk):((0+(test)) ? 1 : -1); }) * 0)
#endif

/* ensure value x is a constant expression */
#ifdef __cplusplus
template<bool,bool> struct CEx_sa;
template<> struct CEx_sa<true,false>{};
template<> struct CEx_sa<false,true>{};
#define CEx(x) (sizeof((CEx_sa<!!(0+(x)), !(0+(x))>())) * 0 + (x))
#else
#define CEx(x) (sizeof(struct { int (CEx):(((0+(x)) && 1) + 1); }) * 0 + (x))
#endif

/* usage like this: */
struct ChkTest {
        int expr1[Chk(3*3) + 1];  // supposed to be [1]
        int expr2 : CEx(3*3);     // supposed to be : 9
};

However, the C++ part of this fails with a parse error already for uses of the Chk macro, at the ) before the * 0 part. (I included the CEx part for completeness, as I’ll need both fixed.)

How can I change these to work with older G++ (GCC) versions? Specifically, these work on Debian etch (G++ 4.1.1) and fail on Debian sargs (G++ 3.3.5) and older.

(Note: I’m a C programmer but don’t really know C++.)

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Update: the precise error message was requested. I saved the snippet above into a file x:

$ gcc -x c -c x
$ gcc -x c++ -c x
x:22: error: parse error before `)' token
x:23: error: parse error before `)' token