Libclang_rt.builtins.a is not being built

Beginners
1

How can I build the file libclang_rt.builtins.a?

I have cloned the LLVM repository and built Clang and the runtimes using the following sequence of commands, but the file libclang_rt.builtins.a is not produced.

cd llvm-project
mkdir ../llvm-and-libcxx-build
cmake -G Ninja -S llvm -B ../llvm-and-libcxx-build -DLLVM_ENABLE_PROJECTS=clang -DLLVM_ENABLE_RUNTIMES=all -DLLVM_RUNTIME_TARGETS=x86_64-unknown-linux-gnu -DCMAKE_BUILD_TYPE=Release
cd ..
ninja -C llvm-and-libcxx-build runtimes
2

llvm/CMakeLists.txt has

set(LLVM_DEFAULT_RUNTIMES "libcxx;libcxxabi;libunwind")

if(LLVM_ENABLE_RUNTIMES STREQUAL "all")
set(LLVM_ENABLE_RUNTIMES ${LLVM_DEFAULT_RUNTIMES})
endif()

so I wonder if you need to list the ones you want explicitly including compiler-rt .