[roll third_party/pigweed] Silence unused argument warnings

moves pw_trace-related build args into imports so toolchains can import
them and silence unused build-arg warnings for downstream projects that
use Pigweed's default host toolchain but don't use pw_trace.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/36080

third_party/pigweed Rolled-Commits: 72b9385372e4b4f..8104e8fabc0b433
CQ-Do-Not-Cancel-Tryjobs: true
Roller-URL: https://ci.chromium.org/b/8853465300289484448
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8853465300289484448
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ia7964b2c1e3bbfe55677c85dc886796dee2eb96a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/36100
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 72b9385..8104e8f 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 72b9385372e4b4f93741c7ca85f570eff25ebeb5
+Subproject commit 8104e8fabc0b4335c7cd87454a9ea24989dff05e