[libc++][CI] Uses LLVM 17 in Docker.

Updates the LLVM versions used in the Dockerfile. It also removes
obsolete symlinks. This doesn't update the Buildkite jobs, they need to
use the new Docker image before they can be updated.

Reviewed By: ldionne, #libc, philnik

Differential Revision: https://reviews.llvm.org/D143007

Author: mordante

libcxx/utils/ci/Dockerfile

@@ -58,31 +58,19 @@ RUN locale-gen
 # LLVM 15, we still need to have Clang 12 in this Docker image because the LLVM
 # 14 release branch CI uses it. The tip-of-trunk CI will never use Clang 12,
 # though.
-ENV LLVM_HEAD_VERSION=16
+ENV LLVM_HEAD_VERSION=17
 RUN apt-get update && apt-get install -y lsb-release wget software-properties-common
 RUN wget https://apt.llvm.org/llvm.sh -O /tmp/llvm.sh
 RUN bash /tmp/llvm.sh $(($LLVM_HEAD_VERSION - 3)) # for CI transitions
 RUN bash /tmp/llvm.sh $(($LLVM_HEAD_VERSION - 2)) # previous release
 RUN bash /tmp/llvm.sh $(($LLVM_HEAD_VERSION - 1)) # latest release
 RUN bash /tmp/llvm.sh $LLVM_HEAD_VERSION          # current ToT
 
-# Make the latest version of Clang the "default" compiler on the system
-# TODO: After branching for LLVM 16, all jobs will be using an
-#       explicitly-versioned version of Clang instead, so we can get rid of
-#       these symlinks.
-RUN ln -fs /usr/bin/clang++-14 /usr/bin/c++ && [ -e $(readlink /usr/bin/c++) ]
-RUN ln -fs /usr/bin/clang-14 /usr/bin/cc && [ -e $(readlink /usr/bin/cc) ]
-
 # Install clang-format; always use the lastest stable branch.
-# TODO LLVM 16 remove hard-coded version 14 and the symlinks
 RUN apt-get update && apt-get install -y clang-format-$(($LLVM_HEAD_VERSION - 2)) clang-format-$(($LLVM_HEAD_VERSION - 1))
-RUN ln -s /usr/bin/clang-format-14 /usr/bin/clang-format && [ -e $(readlink /usr/bin/clang-format) ]
-RUN ln -s /usr/bin/git-clang-format-14 /usr/bin/git-clang-format && [ -e $(readlink /usr/bin/git-clang-format) ]
 
 # 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 $(readlink /usr/bin/clang-tidy) ]
+RUN apt-get update && apt-get install -y clang-tidy-$(($LLVM_HEAD_VERSION - 2)) clang-tidy-$((LLVM_HEAD_VERSION - 1))
 
 # Install llvm-dev and libclang-dev to compile custom clang-tidy checks
 RUN apt-get update && apt-get install -y llvm-$(($LLVM_HEAD_VERSION - 1))-dev     llvm-$(($LLVM_HEAD_VERSION - 2))-dev \