As of clang-11, the most current libc++ is installed tucked away in the llvm-11 libs dir.
There is both a dylib (rpathed) and a static libc++ there. I set this up for now for people like you to use for exactly this. You will have to force it (DYLD_LIBRARY_PATH, possibly static link it, or some other way). It's new. Please feel free to let me know how it works for you. Ken (maintainer of toolchains - clang and libc++, cctools, ld64, tapi - on MacPorts)
