[roll third_party/pigweed] pw_bytes: Add _b suffix for byte literals

This is a frequently requested literal that allows users to easily
create bytes for tests and constants.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/178134

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 5bdcaf22dfa2995..a74535c7d8b644d
Roller-URL: https://ci.chromium.org/b/8766039028730517457
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ied9960e0d95d21fdb6d841f5f4afa39d49a078d2
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/kudzu/+/178211
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 5bdcaf2..a74535c 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 5bdcaf22dfa299539eef552bc4c3d6d5aebc0af1
+Subproject commit a74535c7d8b644d3c36f9d0891dbc59c47e4c3ef