[libc++] Install llvm-16-dev explicitly until LLVM16 is stable

[philnik]

Summary

The clang-tidy checks can't be properly implemented before LLVM16 because the Clang CMake files don't provide the version before.

[Mordante]

LGTM!

libcxx/utils/ci/Dockerfile

 # Install clang-tidy
 # TODO LLVM 16 remove hard-coded version 14 and the symlink
 RUN apt-get update && apt-get install -y clang-tidy-$(($LLVM_HEAD_VERSION - 1)) clang-tidy-$LLVM_HEAD_VERSION clang-tidy-14
 RUN ln -s /usr/bin/clang-tidy-14 /usr/bin/clang-tidy && [ -e $(readlink /usr/bin/clang-tidy) ]
 
 # Install llvm-dev to compile custom clang-tidy checks
 RUN apt-get update && apt-get install llvm-$(($LLVM_HEAD_VERSION - 1))-dev llvm-$(($LLVM_HEAD_VERSION - 2))-dev
 
+# TODO LLVM16 Don't install llvm-16-dev explicitly
+RUN apt-get update && apt-get install llvm-16-dev
+
 # Install clang-tools
 RUN apt-get update && apt-get install -y clang-tools-$(($LLVM_HEAD_VERSION - 1)) clang-tools-$LLVM_HEAD_VERSION
 
 # Install the most recent GCC, like clang install the previous version as a transition.
 ENV GCC_LATEST_VERSION=12
 RUN apt-get update && apt install -y gcc-$((GCC_LATEST_VERSION - 1)) g++-$((GCC_LATEST_VERSION - 1))
 RUN apt-get update && apt install -y gcc-$GCC_LATEST_VERSION g++-$GCC_LATEST_VERSION