Roll libc++ from f8571eaba606 to fc6bbc5eb039 (5 revisions)

https://chromium.googlesource.com/external/github.com/llvm/llvm-project/libcxx.git/+log/f8571eaba606..fc6bbc5eb039

2022-11-02 varconst@apple.com [libc++] Use stack buffers for uninitialized storage in tests.
2022-11-01 koraq@xs4all.nl [libc++] Improves modular build.
2022-11-01 koraq@xs4all.nl [libc++][doc] Updates implementation status.
2022-11-01 koraq@xs4all.nl [libc++][format] Fixes default string alignment.
2022-11-01 koraq@xs4all.nl [libc++] Validates valid weekday indexed range.

If this roll has caused a breakage, revert this CL and stop the roller
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https://autoroll.skia.org/r/libcxx-chromium
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is aware of the problem.

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Tbr: hans@chromium.org,thakis@chromium.org
Change-Id: I205bdfbac18730b08d5b1be60f4677a663f21a56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3999033
Bot-Commit: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1066465}
NOKEYCHECK=True
GitOrigin-RevId: 3cc19836b13b2d9d7d30fe7da80554be90839d47

deps_revisions.gni

@@ -5,5 +5,5 @@
 declare_args() {
   # Used to cause full rebuilds on libc++ rolls. This should be kept in sync
   # with the libcxx_revision vars in //DEPS.
-  libcxx_revision = "f8571eaba606bde2eb8cd34b30104ca33e7c207e"
+  libcxx_revision = "fc6bbc5eb039769b5ed2de84444a3c6f9b45a598"
 }