message: Silence a warning about REALM_VERSION_MAJOR being undefined when
  building realm-js with core v2.8.x.
  Core v3.0 renamed `REALM_VER_MAJOR` to `REALM_VERSION_MAJOR`. If the
  latter isn't defined, we'll #define it to the former so that our version
  checks see the expected core version value.
diff: #include <realm/version.hpp>
  +#ifndef REALM_VERSION_MAJOR
  +#define REALM_VERSION_MAJOR REALM_VER_MAJOR
  +#endif
  +
  #define REALM_HAVE_COMPOSABLE_DISTINCT (REALM_VERSION_MAJOR > 2)
  #if REALM_ENABLE_SYNC
  