varasm.c (struct rtx_const): Change type of un.addr member to struct holding an additional 'symbol' member.

	* varasm.c (struct rtx_const): Change type of un.addr member
	to struct holding an additional 'symbol' member.
	(decode_rtx_const): Re-enable optimization to count SYMBOL_REFs
	with equal string addresses as equal.
	(simplify_subtraction): Adapt to struct rtx_const change.

From-SVN: r64406