[third_party/pigweed] Roll 3 commits

d176d28ac80b3af pw_multibuf: Remove deprecated Chunk::DiscardFront
917922749ee0a18 pw_allocator: Fix data race
6dc5adea0df071c pw_allocator: Add BucketBlockAllocator

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 825f89f0c2fd45d..d176d28ac80b3af
Roller-URL: https://ci.chromium.org/b/8748666450368492033
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I00a53d74420e96aab073fb34c31086e6eb340f19
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/208571
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.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 825f89f..d176d28 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 825f89f0c2fd45dfd38f70eb1a366a4cc70a531b
+Subproject commit d176d28ac80b3af847d7479bbdf3bf2e97943943