roll: pigweed pw_build: Support pw_facade without public headers

- Allow use of pw_facade without public headers, but do not emit a
  .facade subtarget when it is empty. pw_facade still provides value
  since it handles unset backend variables and gives helpful errors.
- Propagate visibility to the ".facade" target. Fix existing visibility
  violations.

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/239755
Original-Revision: b6e84ae48f25f37da692df0b5fcc148ffa9d3d58

Rolled-Repo: https://pigweed.googlesource.com/pigweed/pigweed
Rolled-Commits: dc99cbcc9e8026..b6e84ae48f25f3
Roller-URL: https://ci.chromium.org/b/8735055459885209089
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I145085a217890111029be4925028c53c3121422f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/quickstart/bazel/+/240032
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
diff --git a/MODULE.bazel b/MODULE.bazel
index 410377c..82b7a3f 100644
--- a/MODULE.bazel
+++ b/MODULE.bazel
@@ -49,8 +49,8 @@
     module_name = "pigweed",
     # ROLL: Warning: this entry is automatically updated.
     # ROLL: Last updated 2024-10-03.
-    # ROLL: By https://cr-buildbucket.appspot.com/build/8735061190164687169.
-    commit = "dc99cbcc9e80267da9a19dfd49fdf4be77848a92",
+    # ROLL: By https://cr-buildbucket.appspot.com/build/8735055459885209089.
+    commit = "b6e84ae48f25f37da692df0b5fcc148ffa9d3d58",
     remote = "https://pigweed.googlesource.com/pigweed/pigweed",
 )
 
@@ -58,8 +58,8 @@
     module_name = "pw_toolchain",
     # ROLL: Warning: this entry is automatically updated.
     # ROLL: Last updated 2024-10-03.
-    # ROLL: By https://cr-buildbucket.appspot.com/build/8735061190164687169.
-    commit = "dc99cbcc9e80267da9a19dfd49fdf4be77848a92",
+    # ROLL: By https://cr-buildbucket.appspot.com/build/8735055459885209089.
+    commit = "b6e84ae48f25f37da692df0b5fcc148ffa9d3d58",
     remote = "https://pigweed.googlesource.com/pigweed/pigweed",
     strip_prefix = "pw_toolchain_bazel",
 )