[roll third_party/pigweed] roll: gn

From: git_revision:39a87c0b36310bdf06b692c098f199a0d97fc810
To: git_revision:e0c476ffc83dc10897cb90b45c03ae2539352c5c

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/48760

third_party/pigweed Rolled-Commits: 2713eaa054af73a..21831f286998e27
Roller-URL: https://ci.chromium.org/b/8844497543267286688
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8844497543267286688
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I591d4004dc33409f1916a48d64b70783a27fd206
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/48762
Reviewed-by: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 2713eaa..21831f2 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 2713eaa054af73a22027b136a7bab197de3ba689
+Subproject commit 21831f286998e27f83bcd3dc726a70edfb43b2f1