Revert parts of ADDR_EXPR/CONSTRUCTOR treatment change in match.pd

This reverts the part that substitutes from the definition of an
SSA name to the capture, thus ADDR_EXPR@0 eventually yielding
&y_1->a[i_2] instead of _3.  That's because I didn't think of
how to deal with substituting @0 in the result pattern.  So
the following re-instantiates the SSA def CONSTRUCTOR handling
and in the ADDR_EXPR helpers used by match.pd handles SSA names
defined to ADDR_EXPRs transparently.

	* genmatch.cc (dt_simplify::gen): Revert last change.
	* match.pd: Revert simplification of CONSTUCTOR leaf handling.
	(&x cmp SSA_NAME): Handle ADDR_EXPR in SSA defs.
	* fold-const.cc (split_address_to_core_and_offset): Handle
	ADDR_EXPRs in SSA defs.
	(address_compare): Likewise.