[roll third_party/pigweed] zephyr: Add zephyr's west CLI

Initial Zephyr CLI includes a subcommand 'west manifest' which allows
developers to view the entries that should be added to their west
manifest.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/190547

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 6396cb44478f5b2..8634c8ccc66205c
Roller-URL: https://ci.chromium.org/b/8756078714833763681
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ib9ced2cded56e115919aa0433e605b63257aa0d8
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/192208
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 6396cb4..8634c8c 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 6396cb44478f5b23d747ad5049ae9f4df61ccc85
+Subproject commit 8634c8ccc66205c94302705fdf439a82eb0825fb