roll: pigweed, pw_toolchain: pw_chrono_stl: Move system clock and timer into separate directories

Separate the public_overrides directory for the stl system clock and
system timer backends so one of these backends can be picked up without
bringing the headers of the other backend.

If both system clock and system timer share the same public_overrides
directory, then you can't use a custom system timer with the stl system
clock because the headers of the stl system timer might be picked up by
the compiler before the headers of the custom system timer.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/225992
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https://pigweed.googlesource.com/pigweed/pigweed
pigweed, pw_toolchain Rolled-Commits: 84803f3af2d56dc..c605a3b205089cd
Roller-URL: https://ci.chromium.org/b/8741314076791362865
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: Ibbf7abd558eda184eb65214ef9aac4561db92eae
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/quickstart/bazel/+/226253
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
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/WORKSPACE b/WORKSPACE
index 8dbb648..d223217 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -84,8 +84,8 @@
     name = "pigweed",
     # ROLL: Warning: this entry is automatically updated.
     # ROLL: Last updated 2024-07-26.
-    # ROLL: By https://cr-buildbucket.appspot.com/build/8741324721322295809.
-    commit = "84803f3af2d56dc94596adbbfdcd35836ce46265",
+    # ROLL: By https://cr-buildbucket.appspot.com/build/8741314076791362865.
+    commit = "c605a3b205089cde15f9cafd9af35e8aabf3899e",
     remote = "https://pigweed.googlesource.com/pigweed/pigweed.git",
 )
 
@@ -93,8 +93,8 @@
     name = "pw_toolchain",
     # ROLL: Warning: this entry is automatically updated.
     # ROLL: Last updated 2024-07-26.
-    # ROLL: By https://cr-buildbucket.appspot.com/build/8741324721322295809.
-    commit = "84803f3af2d56dc94596adbbfdcd35836ce46265",
+    # ROLL: By https://cr-buildbucket.appspot.com/build/8741314076791362865.
+    commit = "c605a3b205089cde15f9cafd9af35e8aabf3899e",
     remote = "https://pigweed.googlesource.com/pigweed/pigweed.git",
     strip_prefix = "pw_toolchain_bazel",
 )