* run.1: Document --sysroot=filepath.

	* run.1: Document --sysroot=filepath.
	* sim-options.c (STANDARD_OPTIONS): New member OPTION_SYSROOT.
	(standard_options): Support --sysroot=<path>.
	(standard_option_handler): Handle OPTION_SYSROOT.
	* syscall.c (simulator_sysroot): Define, initialized empty.
	(get_path): Prepend simulator_sysroot to absolute file path.
	[HAVE_STRING_H]: Include string.h.
	[!HAVE_STRING_H && HAVE_STRINGS_H]: Include strings.h.
	* nrun.c [HAVE_UNISTD_H]: Include unistd.h.
	(main): If simulator_sysroot is not empty, chdir there.
	* sim-config.h (simulator_sysroot): Declare.