Make install-runtimes does not install runtimes

I checked out branch 15.0.3 of llvm, and configured the build as such:

cmake -G "Unix Makefiles" -S llvm -B build -DCMAKE_BUILD_TYPE=Release -DLLVM_TARGETS_TO_BUILD=X86 -DCMAKE_INSTALL_PREFIX=/home/me/local -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;lld" -DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx;libcxxabi;libunwind"

I then compiled and installed clang and the runtimes with:

make -C build install
make -C build runtimes
make -C build install-runtimes

I do find clang, lld, etc. in the the directory specified by CMAKE_INSTALL_PREFIX, but no libc++ there. It was built, though, as I can find it in the build directory:

% find . -name

Similarly all the headers are in build/runtimes/runtimes-bins/include/c++/v1.
But I would expect all of these to be installed in the CMAKE_INSTALL_PREFIX directory, just like clang, etc.

What’s the trick?

Does this page help you?
It is slightly different from what you are doing. Note that the INSTALL_PREFIX is missing.

Well, actually, I followed this page, and added CMAKE_INSTALL_PREFIX because I wanted to customize the installation path…
Anyway, I retried, explicitly specifying “-DLLVM_RUNTIME_TARGETS=x86_64-unknown-linux-gnu”, and everything worked fine this time.
(I still have to add “/home/me/local/include/x86_64-unknown-linux-gnu/c++/v1” as an include path for the compiler to find the file “__config_site”, but that’s ok).