Rename "target GNU" -> "target native"

Rename "target GNU" -> "target native"

To be like other native targets.

Leave to_shortname, to_longname, to_doc as inf-child.c sets them:

  t->to_shortname = "native";
  t->to_longname = "Native process";
  t->to_doc = "Native process (started by the \"run\" command).";

gdb/
2014-05-21  Pedro Alves  <palves@redhat.com>

	* gnu-nat.c (gnu): Don't override to_shortname, to_longname or
	to_doc.