Roll libc++ from 92ba6814ab00 to c4fd1bc1c92b (5 revisions)

https://chromium.googlesource.com/external/github.com/llvm/llvm-project/libcxx.git/+log/92ba6814ab00..c4fd1bc1c92b

2025-09-19 ldionne.2@gmail.com [libc++] Improve error resilience when running historical benchmarks
2025-09-18 ldionne.2@gmail.com [libc++] Add a tool to produce historical libc++ benchmark results
2025-09-18 nikolasklauser@berlin.de [libc++] Refactor memory allocation in basic_string (#128423)
2025-09-18 nikolasklauser@berlin.de [libc++] Introduce _LIBCPP_COMPRESSED_ELEMENT (#134253)
2025-09-18 nikolasklauser@berlin.de [libc++] XFAIL regex tests that are currently failing on macOS (#159260)

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/libcxx-chromium
Please CC hans@chromium.org,jwata@google.com,thakis@chromium.org on the revert to ensure that a human
is aware of the problem.

To file a bug in Chromium: https://bugs.chromium.org/p/chromium/issues/entry

To report a problem with the AutoRoller itself, please file a bug:
https://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

Tbr: hans@chromium.org,jwata@google.com,thakis@chromium.org
Change-Id: Ia894717b7578fb7a669abec3e9c30b7b58fe4a89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6968592
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1517931}