[roll third_party/pigweed] pw_allocator: Add BuddyAllocator

This allocator uses buddy memory allocation to allocate power-of-two
sized blocks.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/195952

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: e01ca5820679aeb..6f9099b2b688bf6
Roller-URL: https://ci.chromium.org/b/8749765593167393537
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I921e7a3022522841adf61fc89f23129b2f937276
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/206151
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 e01ca58..6f9099b 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit e01ca5820679aebb2bd99fd7d9490d9cf38048db
+Subproject commit 6f9099b2b688bf63e9480f58b7778ed1d024eb31