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>
9 files changed