[third_party/pigweed] Roll 2 commits

521774e22486af2 pw_allocator: Add UniquePtr<T>
d1cf3b2963745a1 SEED-0112: Async Poll Model

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: a1f371c42bc7e59..521774e22486af2
Roller-URL: https://ci.chromium.org/b/8766688319691944273
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I462f6b360697e26af4d2e0c4e5c3735459a89bf8
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/kudzu/+/177092
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 a1f371c..521774e 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit a1f371c42bc7e593304e5a060ee9475d62396b5a
+Subproject commit 521774e22486af20c57d3c05798fe1b032ef2022