dbxout.c: Remove unnecessary #undefs.

dbxout.c: Remove unnecessary #undefs.

	* dbxout.c: Remove unnecessary #undefs.
	(GDB_INV_REF_REGPARM_STABS_LETTER, DBX_MEMPARM_STABS_LETTER)
	(FILE_NAME_JOINER, STABS_GCC_MARKER): Remove; fold sole
	definition into use sites.
	(cwd): Make local to dbxout_init.
	(dbxout_init): Restructure cwd-using logic for clarity.  Use
	IS_DIR_SEPARATOR.
	* xcoffout.h (DBX_OUTPUT_GCC_MARKER): Definition of
	STABS_GCC_MARKER folded in here.
	* system.h: Poison now-unused macros.
	* doc/tm.texi: Remove documentation of now-unused macros.

From-SVN: r89387