[roll third_party/pigweed] pw_format: Add tests for macro helpers

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/181030

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: a04315b4e778414..6372cdef44d0338
Roller-URL: https://ci.chromium.org/b/8764397261023532849
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I5866566eeaaf450ddf96338b3f51eea80b6d3e33
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/180807
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 a04315b..6372cde 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit a04315b4e77841487f99d99ff3ccd566a96548e3
+Subproject commit 6372cdef44d0338d47108c90c55ad38debcf6c30