pigweed: Initial commit of recipe Create "pigweed" recipe which for now only launches a subbuild. Eventually it will also launch tests using build results. Change-Id: If43d492fce791ec2056df67ed0ea173ded93e857 Bug: 261, 377 Reviewed-on: https://pigweed-review.googlesource.com/c/infra/recipes/+/48422 Commit-Queue: Rob Mohr <mohrr@google.com> Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com> Reviewed-by: Marc-Antoine Ruel <maruel@google.com>