[vm/simdbc] Fix SIMDBC64 build: do not try to generate entry points JSON.
[vm/simdbc] Fix SIMDBC64 build: do not try to generate entry points JSON.

Change-Id: I74d416e345d4dd9c3b73d4fb523ebcf02ca8b629
Reviewed-on: https://dart-review.googlesource.com/43780
Reviewed-by: Martin Kustermann <a35dd5b79fac84b2bb3b026a16b8becc55af5961@google.com>
Reviewed-by: William Hesse <a821cddceae7dc400f272e3cb1a72f400f9fed6d@google.com>
Reviewed-by: Alexander Markov <239e774fd29abc1267878f57afe1a8a03e0ca887@google.com>
Commit-Queue: Vyacheslav Egorov <72c81f38df725d8f1832acb9b5bb99563fc2f1b9@google.com>

dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk