Have the linker report an error if the same script is used twice.

Have the linker report an error if the same script is used twice.

	PR 24576
	* ld/ldfile.c: (ldfile_open_command_file_1): Add new parameter -
	is_script.  If true check that the file has not already been
	parsed as a linker script.
	(ldfile_open_script_file): New function.
	(ldfile_try_open_bfd): Use the new function in place of
	ldfile_open_command_line.
	* ldmain.c (main): Likewise.
	* lexsup.c (parse_args): Use the new function for opening linker
	scripts with the -T option.
	* ldfile.h (ldfile_open_script_file): Add prototype.