[roll third_party/pigweed] pw_docgen: Add rustdoc linking support to pigweed-module tag

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/159292

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 785682ce0a3e86e..2c9efc96d6ba638
Roller-URL: https://ci.chromium.org/b/8774568710691121473
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I3eb1bd6952663ea25a0b3117c9d1767aabd5a9b9
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/159530
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 785682c..2c9efc9 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 785682ce0a3e86ef29b60ca035174a10ba8692ef
+Subproject commit 2c9efc96d6ba6388bf42a78acefcebfb953909a5