[CI] Build newer binutils before building gcc

src/ci/docker/host-x86_64/dist-x86_64-linux/dist.sh

@@ -18,4 +18,16 @@ if [ "${DIST_TRY_BUILD:-0}" == "0" ]; then
     CC=/rustroot/bin/cc CXX=/rustroot/bin/c++ python3 ../x.py dist \
       gcc-dev \
       gcc
+    # We confirm that the built GCC has support for the `retain` attribute.
+    # FIXME: Maybe get the path from `.x.py` instead?
+    gcc_path="./build/$HOSTS/gcc/$HOSTS/install/bin/gcc"
+    c_code='int x __attribute__((used, retain));'
+    if echo "$c_code" | "$gcc_path" -S -x c -o - - | grep -i '"a.*R"'; then
+        echo "retain attribute is supported"
+    else
+        echo "retain attribute is not supported"
+        # We display the generated asm just in case...
+        echo "$c_code" | "$gcc_path" -S -x c -o - -
+        exit 1
+    fi
 fi

src/ci/docker/scripts/build-gcc.sh

@@ -4,6 +4,27 @@ set -eux
 
 source shared.sh
 
+# We have to build our own binutils for the GCC build, because the default CentOS 7 binutils are
+# too old, and they do not support `SHF_GNU_RETAIN`.
+BINUTILS="2.47"
+curl https://ci-mirrors.rust-lang.org/rustc/gcc/binutils-$BINUTILS.tar.xz | xzcat | tar xf -
+mkdir binutils-build
+cd binutils-build
+hide_output ../binutils-$BINUTILS/configure --prefix=/rustroot
+hide_output make -j$(nproc)
+hide_output make install
+
+cd ..
+rm -rf binutils-build binutils-$BINUTILS
+
+if echo '.section .test,"awR",@progbits' | as - -o /dev/null 2>/dev/null; then
+    echo "binutils assembler supports SHF_GNU_RETAIN"
+else
+    echo "binutils assembler DOES NOT support SHF_GNU_RETAIN"
+    exit 1
+fi
+
+
 # Note: in the future when bumping to version 10.1.0, also take care of the sed block below.
 # This version is specified in the Dockerfile
 GCC=$GCC_VERSION
@@ -36,6 +57,7 @@ sed -i'' 's|ftp://gcc\.gnu\.org/pub/gcc/infrastructure|https://ci-mirrors.rust-l
 mkdir ../gcc-build
 cd ../gcc-build
 
+export PATH=/rustroot/bin:$PATH
 # '-fno-reorder-blocks-and-partition' is required to
 # enable BOLT optimization of the C++ standard library,
 # which is included in librustc_driver.so