* target.h (struct gcc_target): Add target_help field.
* target-def.h (TARGET_HELP): New.
  (TARGET_INITIALIZER): Use TARGET_HELP.
* opts.c (command_handle_option): Invoke target_help function, if defined, when the 
  user has specified --target-help on the command line.
* doc/invoke.texi: Mention that --target-help might print additional information.
* doc/tm.texi: Document TARGET_HELP hook.

* arm.c (TARGET_HELP): Override default definition.
  (arm_target_help): New - display a wrapped list of cores and architectures supported.

From-SVN: r126323