feat: add clang to dockerfile and change clang++-19 to clang++

Author: madhav-madhusoodanan

library/stdarch/ci/docker/x86_64-unknown-linux-gnu/Dockerfile

@@ -6,7 +6,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
   make \
   ca-certificates \
   wget \
-  xz-utils
+  xz-utils \
+  clang \
+  lld
 
 RUN wget http://ci-mirrors.rust-lang.org/stdarch/sde-external-9.58.0-2025-06-16-lin.tar.xz -O sde.tar.xz
 RUN mkdir intel-sde

library/stdarch/ci/run.sh

@@ -91,7 +91,7 @@ fi
 case ${TARGET} in
     x86_64-unknown-linux-gnu)
         TEST_CPPFLAGS="-fuse-ld=lld -I/usr/include/x86_64-linux-gnu/"
-        TEST_CXX_COMPILER="clang++-19"
+        TEST_CXX_COMPILER="clang++"
         TEST_RUNNER="${CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUNNER}"
         TEST_SKIP_INTRINSICS=crates/intrinsic-test/missing_x86.txt
         export STDARCH_DISABLE_ASSERT_INSTR=1