ci: try to save some disk space

Author: fw-immunant

build.sh

@@ -12,6 +12,8 @@ cmake -GNinja -DLLVM_ENABLE_PROJECTS="clang" \
     -DLLVM_ENABLE_RUNTIMES="compiler-rt" \
     -DLLVM_DEFAULT_TARGET_TRIPLE="aarch64-linux-gnu" \
     ../llvm
-ninja clang builtins
+ninja clang
+rm -f _CPack_Packages
+ninja builtins
 # copy to expected target triple
 cp -arv lib/clang/19/lib/aarch64-linux-gnu lib/clang/19/lib/aarch64-unknown-linux-gnu