message: Adjust thread name column width depending on real name length.
  Make 16-byte aligned field instead of truncating a name to 16 byte.
diff: @@ -286,7 +286,11 @@ void Log::WriteHeader(llvm::raw_ostream &OS, llvm::StringRef file,
  if (options.Test(LLDB_LOG_OPTION_PREPEND_THREAD_NAME)) {
  llvm::SmallString<32> thread_name;
  llvm::get_thread_name(thread_name);
  - OS << llvm::formatv("{0,-16} ", thread_name);
  +
  + llvm::SmallString<12> format_str;
  + llvm::raw_svector_ostream format_os(format_str);
  + format_os << "{0,-" << llvm::alignTo<16>(thread_name.size()) << "} ";
  + OS << llvm::formatv(format_str.c_str(), thread_name);
  }
  if (options.Test(LLDB_LOG_OPTION_BACKTRACE))
  