[third_party/pigweed] Roll 3 commits

a56e966f863779b pw_build: Fix using pw_cc_blob_library target in e
de74460373ec62a pw_string: Add ToString for iterables
cda2a749853a894 SEED-0128: Claim SEED number

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 1807af542686e6d..a56e966f863779b
Roller-URL: https://ci.chromium.org/b/8749648350385823985
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I06eafecd7f625d15deba683ac9f71335d1125fac
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/quickstart/bazel/+/206750
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 1807af5..a56e966 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 1807af542686e6dfe1dad3bb9c21d17d1c88a0da
+Subproject commit a56e966f863779b21b263c81c1002b5dd4ee5841