Type Library do contain a x86 vs x64 flag in the SYSKIND enumeration. In fact it even supports 16 bits Windows. It can be read using the ITypeLib::GetLibAttr method, something like this:

int _tmain(int argc, _TCHAR* argv[])
{
    CoInitialize(NULL);

    CComPtr<ITypeLib> tlb;
    LoadTypeLib(L"C:\\myPath\\MyFile.tlb", &tlb);
    TLIBATTR *patt;
    tlb->GetLibAttr(&patt);
    switch(patt->syskind)
    {
        case SYSKIND::SYS_WIN64:
            printf("WIN64");
            break;

        case SYSKIND::SYS_WIN32:
            printf("WIN32");
            break;

        case SYSKIND::SYS_WIN16:
            printf("WIN16");
            break;
    }
    tlb->ReleaseTLibAttr(patt);

    CoUninitialize();
}

Note SYSKIND is not a flags, it's an enum, you don't have something like "any CPU" value.