[roll third_party/pigweed] pw_thread: Add explicit public default ctor for stl::Options

Without the explicit default public constructor c++20-based compiler
rejects `stl::Options{}` initialization and allows only `stl::Options()`
one.
See this example for the reference: https://godbolt.org/z/K5GWaGsTf.

This CL also prevents to create `thread::Options` using `{}` syntax
with explicitly defining the empty constructor instead of the default
one.
See this example for the reference: https://godbolt.org/z/EP7hTooo8.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/98101

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 672047a6d01ffb2..2bc2d9b4ea8fe26
Roller-URL: https://ci.chromium.org/b/8810829835870525617
Cq-Cl-Tag: roller-builder:pigweed-experimental-roller
Cq-Cl-Tag: roller-bid:8810829835870525617
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I0046e268c6b4b7d339c0226b5fa22c623f377b90
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/98844
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 672047a..2bc2d9b 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 672047a6d01ffb265e207f05e8f132cb716c6e7b
+Subproject commit 2bc2d9b4ea8fe26d5ff8b4a19b3886b64a24635e