roll: third_party/pigweed pw_build: Add helper for Pigweed-specific conditions

This helper allows Pigwed to write `if` conditions that gate build file
logic from propagating to downstream.

Original-Bug: b/409847680
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/282936
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Original-Revision: baa8c724cf679dd071e7bef4294f59838f63c3b7

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: 67b5300fd9a6b4..baa8c724cf679d
Roll-Count: 1
Roller-URL: https://cr-buildbucket.appspot.com/build/8717574067768329937
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I080404044bf9115e5add34785cc4e2855ef719f6
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/283933
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 67b5300..baa8c72 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 67b5300fd9a6b4bb6749a6485d73b3229bd6aa40
+Subproject commit baa8c724cf679dd071e7bef4294f59838f63c3b7