GCC 3.4.3, __sync_fetch_and_add on SunOS 5.10 sparc

GCC 3.4.3 is the default compiler which ships with Solaris 10 (SunOS 5.10).This compiler compiles pdns-3.1 with a couple of patches here and there more or less fine on the i86pc platform (32- and 64-bit x86).
However, on sparc, the compilation fails because GCC 3.4.3 does not include the __sync_fetch_and_add() function (macro?).
On i86pc, the compilation passes because of this bit of code:
    // the below is necessary because __sync_fetch_and_add is not universally available on i386.. I 3> RHEL5.    #if defined( __GNUC__ ) && ( defined( __i386__ ) || defined( __x86_64__ ) )    static int atomic_exchange_and_add( unsigned int * pw, int dv )    {        // int r = *pw;        // *pw += dv;        // return r;
        int r;
        __asm__ __volatile__        (            "lock\n\t"            "xadd %1, %0":            "+m"( *pw ), "=r"( r ): // outputs (%0, %1)            "1"( dv ): // inputs (%2 == %1)            "memory", "cc" // clobbers        );
        return r;    }
Obviously, the x86 assembler bit cannot work on sparc, and since the __sync_fetch_and_add() is unavailable, it fails.
My "fix" for that was this:
    #else    static int atomic_exchange_and_add( unsigned int * pw, int dv )    {      #if(((__GNUC__ == 3) && (__GNUC_MINOR__ == 4) && (__GNUC_PATCHLEVEL__ == 3)) && defined(__sparc__))      int r = *pw;      *pw += dv;      return(r);      #else      return __sync_fetch_and_add(pw, dv);      #endif    }    #endif
But I do not trust myself to have fully understood the code and the intent. Can someone who has worked on this code confirm or deny that this is a sane fix?

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