Allow old toolchain on some images

LLVM 16 will require GCC >= 7.1. For now, set the flag that
allows using an older toolchain.

Author: nikic

src/ci/docker/host-x86_64/arm-android/Dockerfile

@@ -29,7 +29,8 @@ ENV PATH=$PATH:/android/sdk/platform-tools
 
 ENV TARGETS=arm-linux-androideabi
 
-ENV RUST_CONFIGURE_ARGS --arm-linux-androideabi-ndk=/android/ndk/arm-14
+ENV RUST_CONFIGURE_ARGS --arm-linux-androideabi-ndk=/android/ndk/arm-14 \
+    --set llvm.allow-old-toolchain
 
 ENV SCRIPT python3 ../x.py --stage 2 test --host='' --target $TARGETS
 

src/ci/docker/host-x86_64/dist-android/Dockerfile

@@ -32,7 +32,8 @@ ENV RUST_CONFIGURE_ARGS \
       --i686-linux-android-ndk=/android/ndk/x86-14 \
       --aarch64-linux-android-ndk=/android/ndk/arm64-21 \
       --x86_64-linux-android-ndk=/android/ndk/x86_64-21 \
-      --disable-docs
+      --disable-docs \
+      --set llvm.allow-old-toolchain
 
 ENV SCRIPT python3 ../x.py dist --host='' --target $TARGETS
 

src/ci/docker/host-x86_64/dist-i586-gnu-i586-i686-musl/Dockerfile

@@ -36,7 +36,8 @@ RUN /scripts/cmake.sh
 ENV RUST_CONFIGURE_ARGS \
       --musl-root-i586=/musl-i586 \
       --musl-root-i686=/musl-i686 \
-      --disable-docs
+      --disable-docs \
+      --set llvm.allow-old-toolchain
 
 # Newer binutils broke things on some vms/distros (i.e., linking against
 # unknown relocs disabled by the following flag), so we need to go out of our

src/ci/docker/host-x86_64/dist-mips-linux/Dockerfile

@@ -26,5 +26,6 @@ RUN /scripts/cmake.sh
 
 ENV HOSTS=mips-unknown-linux-gnu
 
-ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs
+ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs \
+    --set llvm.allow-old-toolchain
 ENV SCRIPT python3 ../x.py dist --host $HOSTS --target $HOSTS

src/ci/docker/host-x86_64/dist-mips64-linux/Dockerfile

@@ -25,5 +25,6 @@ RUN /scripts/cmake.sh
 
 ENV HOSTS=mips64-unknown-linux-gnuabi64
 
-ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs
+ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs \
+    --set llvm.allow-old-toolchain
 ENV SCRIPT python3 ../x.py dist --host $HOSTS --target $HOSTS

src/ci/docker/host-x86_64/dist-mips64el-linux/Dockerfile

@@ -26,5 +26,6 @@ RUN /scripts/cmake.sh
 
 ENV HOSTS=mips64el-unknown-linux-gnuabi64
 
-ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs
+ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs \
+    --set llvm.allow-old-toolchain
 ENV SCRIPT python3 ../x.py dist --host $HOSTS --target $HOSTS

src/ci/docker/host-x86_64/dist-mipsel-linux/Dockerfile

@@ -25,5 +25,6 @@ RUN /scripts/cmake.sh
 
 ENV HOSTS=mipsel-unknown-linux-gnu
 
-ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs
+ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs \
+    --set llvm.allow-old-toolchain
 ENV SCRIPT python3 ../x.py dist --host $HOSTS --target $HOSTS

src/ci/docker/host-x86_64/dist-x86_64-netbsd/Dockerfile

@@ -21,5 +21,6 @@ ENV \
 
 ENV HOSTS=x86_64-unknown-netbsd
 
-ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs
+ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs \
+    --set llvm.allow-old-toolchain
 ENV SCRIPT python3 ../x.py dist --host $HOSTS --target $HOSTS

src/ci/docker/host-x86_64/i686-gnu-nopt/Dockerfile

@@ -27,6 +27,7 @@ RUN mkdir -p /config
 RUN echo "[rust]" > /config/nopt-std-config.toml
 RUN echo "optimize = false" >> /config/nopt-std-config.toml
 
-ENV RUST_CONFIGURE_ARGS --build=i686-unknown-linux-gnu --disable-optimize-tests
+ENV RUST_CONFIGURE_ARGS --build=i686-unknown-linux-gnu --disable-optimize-tests \
+    --set llvm.allow-old-toolchain
 ENV SCRIPT python3 ../x.py test --stage 0 --config /config/nopt-std-config.toml library/std \
   && python3 ../x.py --stage 2 test

src/ci/docker/host-x86_64/i686-gnu/Dockerfile

@@ -23,7 +23,8 @@ RUN sh /scripts/sccache.sh
 COPY scripts/cmake.sh /scripts/
 RUN /scripts/cmake.sh
 
-ENV RUST_CONFIGURE_ARGS --build=i686-unknown-linux-gnu
+ENV RUST_CONFIGURE_ARGS --build=i686-unknown-linux-gnu \
+    --set llvm.allow-old-toolchain
 # Exclude some tests that are unlikely to be platform specific, to speed up
 # this slow job.
 ENV SCRIPT python3 ../x.py --stage 2 test \