Use _() in calls to build_help

Use _() in calls to build_help

Currently some code in gdb uses build_help with N_(), like:

  static const std::string compile_print_help
    = gdb::option::build_help (N_("\

I believe this is incorrect.  The N_ macro is used to mark text that
should end up in the message catalog, but which will be translated by
a later call to gettext.

However, in this case, there is no later call to gettext, so (if gdb
had translations), this text would remain untranslated.

Instead, I think using the ordinary _() macro is correct here.
Translators will have to know to preserve "%OPTIONS%" in the text --
but that seems both unavoidable and fine.

Tested by rebuilding as there's not much else to do.

gdb/ChangeLog
2019-08-05  Tom Tromey  <tromey@adacore.com>

	* compile/compile.c (_initialize_compile): Use _(), not N_().
	* thread.c (_initialize_thread): Use _(), not N_().
	* stack.c (_initialize_stack): Use _(), not N_().
	* printcmd.c (_initialize_printcmd): Use _(), not N_().