Fix recent thinko in operand_equal_p

Fix recent thinko in operand_equal_p

There is a thinko in a recent improvement made to operand_equal_p where
the code just looks at operand 2 of COMPONENT_REF, if it is present, to
compare addresses.  That's wrong because operand 2 contains the number of
DECL_OFFSET_ALIGN-bit-sized words so, when DECL_OFFSET_ALIGN > 8, not all
the  bytes are included and some of them are in DECL_FIELD_BIT_OFFSET, see
get_inner_reference for the model computation.

In other words, you would need to compare operand 2 and DECL_OFFSET_ALIGN
and DECL_FIELD_BIT_OFFSET in this situation, but I'm not sure this is worth
the hassle in practice so the fix just removes this alternate handling.

gcc/
	* fold-const.cc (operand_compare::operand_equal_p) <COMPONENT_REF>:
	Do not take into account operand 2.
	(operand_compare::hash_operand) <COMPONENT_REF>: Likewise.

gcc/testsuite/
	* gnat.dg/opt99.adb: New test.
	* gnat.dg/opt99_pkg1.ads, gnat.dg/opt99_pkg1.adb: New helper.
	* gnat.dg/opt99_pkg2.ads: Likewise.