I haven't seen this before... llvm 15, 16, and 17 all compiled for me.
CMake Error at /llvm-project-18.1.0.src/libc/cmake/modules/LLVMLibCObjectRules.cmake:703 (target_link_libraries):
Target "libc.src.errno.errno" of type UTILITY may not be linked into
another target. One may link only to INTERFACE, OBJECT, STATIC or SHARED
libraries, or to executables with the ENABLE_EXPORTS property set.
Call Stack (most recent call first):
/llvm-project-18.1.0.src/libc/cmake/modules/LLVMLibCObjectRules.cmake:805 (create_entrypoint_object)
/llvm-project-18.1.0.src/libc/cmake/modules/LLVMLibCObjectRules.cmake:883 (expand_flags_for_entrypoint_object)
/llvm-project-18.1.0.src/libc/src/stdlib/CMakeLists.txt:34 (add_entrypoint_object)