[roll third_party/pigweed] pw_build: Don't evaluate path expressions in-place

This updates the pw_evaluate_path_expressions GN template to write its
output to a different file from the source. This is done to avoid
changing the contents of a file the build graph depends on, preventing
build steps from re-running unnecessarily.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/126912

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 3ba0e951a04309c..6d22d50628dbc7b
Roller-URL: https://ci.chromium.org/b/8790959490812194705
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ibc4e6513f4e36a99402fa22117c4f9c68336d63d
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/126899
Bot-Commit: 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 3ba0e95..6d22d50 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 3ba0e951a04309c5232ef2aa469dfee36ac4a3a1
+Subproject commit 6d22d50628dbc7b90d7786701f9391c3b54fa60a