* system.h: Include filenames.h.
	(IS_DIR_SEPARATOR, IS_ABSOLUTE_PATHNAME): Don't define.
	(DIR_SEPARATOR, DIR_SEPARATOR_2): If not already defined,
	define based on HAVE_DOS_BASED_FILE_SYSTEM.
	* config/i386/xm-cygwin.h, config/i386/xm-djgpp.h
	* config/i386/xm-mingw32.h: Don't define
	HAVE_DOS_BASED_FILE_SYSTEM,
	DIR_SEPARATOR, or DIR_SEPARATOR_2.
	* doc/hostconfig.texi: Update to match.

	* cppfiles.c, gcc.c, gensupport.c, protoize.c,
	config/i386/cygwin.h:
	Use IS_ABSOLUTE_PATH throughout.
	* gcc.c (DIR_UP): Delete, unused.
	* protoize.c (IS_SAME_PATH): Define in terms of
	FILENAME_CMP.
	(is_abspath): Delete.
java:
	* jcf-path.c: Don't default-define PATH_SEPARATOR nor
	DIR_SEPARATOR.
	Use FILENAME_CMP.
	* jcf-write.c: Don't default-define DIR_SEPARATOR.
	* jcf.h: Delete COMPARE_FILENAMES definition.

From-SVN: r68863