[PATCH v3] match.pd: Add pattern to simplify `(a - 1) & -a` to `0`

Thank you for the feedback. I have made the minor changes that were requested.
Additionally, I extracted the repetitive code into a reusable helper function,
match_plus_neg_pattern, making the code much more readable. Furthermore, the
logic, code, and tests remain the same as in version 2 of the patch.

gcc/ChangeLog:

	* match.pd: New pattern.
	* simplify-rtx.cc (match_plus_neg_pattern): New helper function.
	(simplify_context::simplify_binary_operation_1): New
	code to handle (a - 1) & -a, (a - 1) | -a and (a - 1) ^ -a.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/bitops-11.c: New test.