cmake HAVE_LLVM_LIBC examples

Lewuathe/mlir-hello thirdparty/llvm-project/llvm/cmake/modules/HandleLLVMOptions.cmake :1420 

check_library_exists(llvmlibc printf "" HAVE_LLVM_LIBC)

root-project/root interpreter/llvm-project/llvm/cmake/modules/HandleLLVMOptions.cmake :1375 

check_library_exists(llvmlibc printf "" HAVE_LLVM_LIBC)