[debugserver] Add --version/-V command line option to debugserver.

[JDevlieghere]

Summary

When not running under a TTY the output is buffered and not flushed
before debugserver exits which makes it impossible to parse the version
string. This adds a -V/--version command that just prints the version
to stdout and exits with an exit code zero.

[jasonmolenda]

Hm, if the goal is to get -version (an unrecognized cmd line option) to explicitly print to stderr, don't we want to change the lines in show_usage_and_exit? I think this change would result in us not getting the version string in console logs for normal debug sessions, where we want to keep it.

[jasonmolenda]

Awesome.

[aprantl]

Good catch!

lldb/tools/debugserver/source/debugserver.cpp

#endif
   if (DNBLogEnabled()) {
     for (i = 0; i < argc; i++)
       DNBLogDebug("argv[%i] = %s", i, argv[i]);
   }
 
   // as long as we're dropping remotenub in as a replacement for gdbserver,
   // explicitly note that this is not gdbserver.
 
-  RNBLogSTDOUT("%s-%s %sfor %s.\n", DEBUGSERVER_PROGRAM_NAME,
-               DEBUGSERVER_VERSION_STR, compile_options.c_str(), RNB_ARCH);
+  fprintf(stderr, "%s-%s %sfor %s.\n", DEBUGSERVER_PROGRAM_NAME,
 
   std::string host;
   int port = INT32_MAX;
   char str[PATH_MAX];
   str[0] = '\0';
 
   if (g_lockdown_opt == 0 && g_applist_opt == 0 && communication_fd == -1) {
     // Make sure we at least have port