[libc++] CI: Run -std=c++03 on Clang ToT

Differential Revision: https://reviews.llvm.org/D106104

libcxx/utils/ci/Dockerfile

@@ -38,7 +38,6 @@ RUN apt-get update && apt-get install -y bash curl
 # Install various tools used by the build or the test suite
 RUN apt-get update && apt-get install -y ninja-build python3 python3-sphinx python3-distutils git gdb
 RUN apt-get update && apt-get install -y libc6-dev-i386 # Required to cross-compile to 32 bits
-RUN echo
 
 # Install Clang <latest>, <latest-1> and ToT, which are the ones we support.
 ENV LLVM_LATEST_VERSION=12

libcxx/utils/ci/run-buildbot

@@ -187,9 +187,6 @@ check-generated-output)
     python3 libcxx/utils/graph_header_deps.py >/dev/null
 ;;
 generic-cxx03)
-    # TODO: Switch to compiling with Clang ToT once issues with https://reviews.llvm.org/D104500 are resolved.
-    export CC=clang-12
-    export CXX=clang++-12
     clean
     generate-cmake -C "${MONOREPO_ROOT}/libcxx/cmake/caches/Generic-cxx03.cmake" \
                    -DLIBCXX_TEST_CONFIG="${MONOREPO_ROOT}/libcxx/test/configs/libcxx-trunk-shared.cfg.in"