[vm] Use SDK_DIR in precompiler2 when locating dart.
[vm] Use SDK_DIR in precompiler2 when locating dart.

Change-Id: I216c126a7a6953fd6f8eb1b060e27eddfafb332b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/168102
Auto-Submit: Jonas Termansen <092ec58085ae5e368bc39d18752740ff81a2d09c@google.com>
Commit-Queue: Jonas Termansen <092ec58085ae5e368bc39d18752740ff81a2d09c@google.com>
Commit-Queue: Vyacheslav Egorov <72c81f38df725d8f1832acb9b5bb99563fc2f1b9@google.com>
Reviewed-by: Vyacheslav Egorov <72c81f38df725d8f1832acb9b5bb99563fc2f1b9@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk