[roll third_party/pigweed] pw_build: Support symlinks in mirror_tree.py

The source path needs to be resolved before linking it in case it is a
symlink.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/39220

third_party/pigweed Rolled-Commits: 4e6d038872b3a54..c02188cf65aa034
Roller-URL: https://ci.chromium.org/b/8851851256674267952
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8851851256674267952
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ie9861146afbd78d3d9815e1fc672fb4ce8055d39
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/39260
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 4e6d038..c02188c 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 4e6d038872b3a54c30a8d383c01ce8c0c4bd18d0
+Subproject commit c02188cf65aa03440f575cc24c40b1ae41331e98