* Makefile.in (CFILES): Add lrealpath.c.

	* Makefile.in (CFILES): Add lrealpath.c.
	(REQUIRED_OFILES): Add lrealpath.o.
	(lrealpath.o): Add rule.
	* aclocal.m4 (libiberty_NEED_DECLARATION): Add.
	* configure.in: Add realpath and canonicalize_file_name to
	checkfuncs and AC_CHECK_FUNCS.  Use libiberty_NEED_DECLARATION
	for canonicalize_file_name.
	* lrealpath.c: New file.
	* make-relative-prefix.c: Update documentation.
	(make_relative_prefix): Simplify.  Use lbasename and lrealpath.
	* config.in: Regenerated.
	* configure: Regenerated.
	* functions.texi: Regenerated.