[roll third_party/pigweed] pw_toolchain: Rename `action_config_flag_sets` to `flag_sets`

Updates all docs and references of `action_config_flag_sets` to
`flag_sets`. Nobody was using this name previously.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/192911

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 6532d77de01bf38..a2b21f201273691
Roller-URL: https://ci.chromium.org/b/8755709034097609313
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I76b41d2235ff6e716ef6594ac3bc6de8b72ed8b0
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/examples/+/193150
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 6532d77..a2b21f2 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 6532d77de01bf3809ed41534e609802198e84dca
+Subproject commit a2b21f20127369137c0a24ba1aa91dba86ce9197