Keep readelf (#13105)

Author: jonathanmetzman

infra/base-images/base-clang/checkout_build_install_llvm.sh

@@ -149,6 +149,7 @@ function free_disk_space {
       /usr/local/bin/llvm-ranlib \
       /usr/local/bin/llvm-symbolizer \
       /usr/local/bin/llvm-undname \
+      /usr/local/bin/llvm-readelf \
       $LLVM_TOOLS_TMPDIR
 
     # Delete remaining llvm- binaries.