[roll third_party/pigweed] pw_allocator/cmake: Add CMake support

This change adds CMake support to pw_allocator module.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/126630

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 809a423d7ddf0d2..78ad6403cc67600
Roller-URL: https://ci.chromium.org/b/8791412368491178881
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ie87fa2ce1fca607b75ec4c4273962cfd65569bbf
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/126794
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 809a423..78ad640 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 809a423d7ddf0d288718050f7ec3e18fff477e78
+Subproject commit 78ad6403cc6760021e89e8bb9b6c27c54af29f33