Not sure how helpful this is, but the following code compiles fine for me (VC 12.0 and 14.0):

#include <stdio.h>

char myStr[];
struct { char* a; } myStruct = { myStr };

int main() {
    printf("%s", myStruct.a);
    return 0;
}

static char myStr[] = "123456789";

Any reason you can't define the forward definition like this? (It only seems to work with myStr[] and not *myStr, for some reason.)