This appears to be a bug in the gcc that we're currently using.

Compiling this, with -O:

const int i;
int f(void) {return i;}

results in this assembly:

        pushl   %ebp
        movl    %esp, %ebp
        movl    $0, %eax   <--- the $0 is wrong, should be _i
        leave
        ret

Turning off -O makes it work.

Maybe time to update our mingw gcc bundles?