[roll third_party/pigweed] pw_{rpc, sync_stl}: Assert if STL mutex is misused

- Update the pw_sync_stl mutex to track whether it is locked and assert
  if it's used improperly. The C++ standard states that unlocking an
  unlocked mutex is undefined behavior. Neither libc++ nor libstdc++
  crash when a mutex is unlocked multiple times (at least on Linux).
- Annotate the stub pw::rpc::internal::LockGuard class with thread
  safety annotations so that thread safety analysis applies when
  compiling without RPC locking.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/77504

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: e4a0a67c425eec9..d7f76fa1614667c
Roller-URL: https://ci.chromium.org/b/8825312104141739057
Cq-Cl-Tag: roller-builder:pigweed-sample-project-roller
Cq-Cl-Tag: roller-bid:8825312104141739057
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Id41b2b739d55aa2e264909bf51fc709777de558b
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/sample_project/+/78060
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index e4a0a67..d7f76fa 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit e4a0a67c425eec93c924d83edb446572f9ab4277
+Subproject commit d7f76fa1614667c4cacc1cffa17d86b3e3a5394d