Add a new option to the linker: --error-handling-script=<NAME>. Run the script ...

Add a new option to the linker: --error-handling-script=<NAME>.  Run the script <NAME> if an undefined symbol or unfound library error is encountered.

	PR 26626
	* ldmain.c (undefined_symbol): If an error handlign script is
	available, call it.
	* ldfile.c  (error_handling_script): Declare.
	(ldfile_open_file): If a library cannot be found and an error
	handling script is available, call it.
	* ldmain.h  (error_handling_script): Prototype.
	* ldlex.h (OPTION_ERROR_HANDLING_SCRIPT): Define.
	* lexsup.c (ld_options): Add --error-handling-script.
	(parse_args): Add support for --errror-handling-script.
	* ld.texi: Document the new feature.
	* configure.ac: Add --error-handling-script option to disable
	support for the new feature.
	* NEWS: Mention the new feature.
	* config.in: Regenerate.
	* configure: Regenerate.