dds_aot.dart.snapshot was not being generated for runtime build targets,
and dds.dart.snapshot was being built regardless of whether or not we
were building for an IA32 target.
This change also adds a check for IA32 in 'dart run' so the "Could not
find dds_aot.dart.snapshot. Have you built the full Dart SDK?" message
isn't printed when we fall back to using dds.dart.snapshot.
This change also reverts 2cc08595a6, which
failed to fix the issue it was attempting to fix.
TEST=pkg/vm_service tests
Change-Id: Ic990082c25b0d022093ad66600332dfb2878709f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/341760
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Ben Konyi <bkonyi@google.com>
0a393f1b69