[roll third_party/pigweed] pw_assert_log: Fix Soong rules

The the Soong pw_assert_log_defaults cc_defaults was incorrectly using
pw_log_null as the log backend. This redirects all PW_LOG* calls to a
no-op function, breaking PW_CHECK, PW_ASSERT and friends who depend on
that. This would mean that code continued executing after a crash!

Do not let defaults inject backends, especially the pw_log_null backend.

Original-Bug: 324266698

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/190602

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: bb1870ce1c8d99a..8b408829fcd8b9d
Roller-URL: https://ci.chromium.org/b/8755970041828064817
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I875fb71d4918b1e6b7ceb02ff9e8e260fa58e22b
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/192785
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 bb1870c..8b40882 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit bb1870ce1c8d99afe0fdf87212a0f19337572ee9
+Subproject commit 8b408829fcd8b9d74d49bf0f2d23554a7461e3b6