[roll third_party/pigweed] pw_toolchain: Optionally depend on pw_env_setup_CIPD_PIGWEED

Changes clang_tools.gni to only generate a relative path prefix for
CIPD-provided tools if pw_env_setup_CIPD_PIGWEED is set.

Original-Bug: b/294886611
Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/163790

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 212145181448f45..02f2811d2c47ad6
Roller-URL: https://ci.chromium.org/b/8773305185909115121
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Iffa1466398bdb4b56c329fdbaddbe5ff2e739e98
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/163970
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 2121451..02f2811 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 212145181448f4512f4b9cca4e4d1eecf3e2d8a7
+Subproject commit 02f2811d2c47ad6fbb029c7b48c82f757cc4ec4a