[roll third_party/pigweed] pw_system: Move STL main() to toolchain

pw_system stashed a main() implementation in stl_target_hooks.cc,
which was a bit of a kludge and caused some downstream challenges.

This commit moves that main() implementation to the
host_device_simulator toolchain, which also improves symmetry between
targets.

Longer term, that main() implementation may want to move to a
newly-created pw_boot_stl module to further improve symmetry.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/122830

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: c1b756aee6cffed..4f3608a2d723d4d
Roller-URL: https://ci.chromium.org/b/8795408574173086561
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I2573ef7ec5a42420be5d4c3b42ac07afdf342337
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/122991
Commit-Queue: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
Bot-Commit: Pigweed Integration Roller <pigweed-integration-roller@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index c1b756a..4f3608a 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit c1b756aee6cffed037ac3f2566e1718e2b2e649d
+Subproject commit 4f3608a2d723d4de6dc46b2a52690da7d5c465d3