[roll third_party/pigweed] pw_build: Make build warnings configurable in CMake

Allow configuring which warnings to use in builds with the
pw_build_WARNINGS variable.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/79480

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 6b582970e1b81d2..c4e9c62a8e6b36d
Roller-URL: https://ci.chromium.org/b/8824490278711912657
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8824490278711912657
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Iababde9fa95c7c8aad3a8e8e72e9f576241ff0d7
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/80101
Bot-Commit: 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 6b58297..c4e9c62 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 6b582970e1b81d2406f360f63365af29f8a39fc6
+Subproject commit c4e9c62a8e6b36d0deac9fea6bfb85059bedadd0