Fix cg_gcc CI run

src/ci/docker/host-x86_64/x86_64-gnu-llvm-16/Dockerfile

@@ -37,6 +37,9 @@ RUN curl -sL "https://github.com/PowerShell/PowerShell/releases/download/v7.3.1/
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
+# Make `libgccjit.so` accessible to the linker.
+RUN ln -s /usr/lib/gcc/x86_64-linux-gnu/12/libgccjit.so /usr/lib/x86_64-linux-gnu/libgccjit.so
+
 # We are disabling CI LLVM since this builder is intentionally using a host
 # LLVM, rather than the typical src/llvm-project LLVM.
 ENV NO_DOWNLOAD_CI_LLVM 1
@@ -50,7 +53,6 @@ ENV RUST_CONFIGURE_ARGS \
       --build=x86_64-unknown-linux-gnu \
       --llvm-root=/usr/lib/llvm-16 \
       --enable-llvm-link-shared \
-      $USE_NEW_MANGLING \
       --set rust.thin-lto-import-instr-limit=10
 
 COPY host-x86_64/x86_64-gnu-llvm-16/script.sh /tmp/

src/ci/docker/host-x86_64/x86_64-gnu-llvm-17/Dockerfile

@@ -46,7 +46,6 @@ ENV RUST_CONFIGURE_ARGS \
       --build=x86_64-unknown-linux-gnu \
       --llvm-root=/usr/lib/llvm-17 \
       --enable-llvm-link-shared \
-      $USE_NEW_MANGLING \
       --set rust.thin-lto-import-instr-limit=10
 
 COPY host-x86_64/x86_64-gnu-llvm-16/script.sh /tmp/

src/ci/docker/run.sh

@@ -270,11 +270,6 @@ touch $objdir/${SUMMARY_FILE}
 extra_env=""
 if [ "$ENABLE_GCC_CODEGEN" = "1" ]; then
   extra_env="$extra_env --env ENABLE_GCC_CODEGEN=1"
-  # If `ENABLE_GCC_CODEGEN` is set and not empty, we add the `--enable-new-symbol-mangling`
-  # argument to `RUST_CONFIGURE_ARGS` and set the `GCC_EXEC_PREFIX` environment variable.
-  # `cg_gcc` doesn't support the legacy mangling so we need to enforce the new one
-  # if we run `cg_gcc` tests.
-  extra_env="$extra_env --env USE_NEW_MANGLING=--enable-new-symbol-mangling"
   # Fix rustc_codegen_gcc lto issues.
   extra_env="$extra_env --env GCC_EXEC_PREFIX=/usr/lib/gcc/"
   echo "Setting extra environment values for docker: $extra_env"

src/ci/run.sh

@@ -163,6 +163,14 @@ if [ "$IS_NOT_LATEST_LLVM" = "" ]; then
   export COMPILETEST_NEEDS_ALL_LLVM_COMPONENTS=1
 fi
 
+if [ "$ENABLE_GCC_CODEGEN" = "1" ]; then
+  # If `ENABLE_GCC_CODEGEN` is set and not empty, we add the `--enable-new-symbol-mangling`
+  # argument to `RUST_CONFIGURE_ARGS` and set the `GCC_EXEC_PREFIX` environment variable.
+  # `cg_gcc` doesn't support the legacy mangling so we need to enforce the new one
+  # if we run `cg_gcc` tests.
+  RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --enable-new-symbol-mangling"
+fi
+
 # Print the date from the local machine and the date from an external source to
 # check for clock drifts. An HTTP URL is used instead of HTTPS since on Azure
 # Pipelines it happened that the certificates were marked as expired.