roll: third_party/pigweed pw_toolchain: llvm_clang.BUILD -> llvm_clang_legacy.BUILD part 2/2

Finishes movement of llvm_clang.BUILD to llvm_clang_legacy.BUILD in
preparation for the migration to rules_cc toolchains.

Original-Bug: b/346388161
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/232216
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Original-Revision: 176d86a6da5e58e19e3f49818bf3d703d985a37c

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: 01f0043a5cb359..176d86a6da5e58
Roller-URL: https://ci.chromium.org/b/8736506170990055601
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I067dafdfd93de5da7835f6641c2e75bcb994f83d
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/236633
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
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 01f0043..176d86a 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 01f0043a5cb359444f60d4202675cd124398e9e7
+Subproject commit 176d86a6da5e58e19e3f49818bf3d703d985a37c