Fix PR tree-optimization/63184: add simplification of (& + A) != (& + B)

Fix PR tree-optimization/63184: add simplification of (& + A) != (& + B)

These two testcases have been failing since GCC 5 but things
have improved such that adding a simplification to match.pd
for this case is easier than before.
In the end we have the following IR:
....
  _5 = &a[1] + _4;
  _7 = &a + _13;
  if (_5 != _7)

So we can fold the _5 != _7 into:
(&a[1] - &a) + _4 != _13

The subtraction is folded into constant by ptr_difference_const.
In this case, the full expression gets folded into a constant
and we are able to remove the if statement.

OK? Bootstrapped and tested on aarch64-linux-gnu with no regressions.

gcc/ChangeLog:

	PR tree-optimization/63184
	* match.pd: Add simplification of pointer_diff of two pointer_plus
	with addr_expr in the first operand of each pointer_plus.
	Add simplificatoin of ne/eq of two pointer_plus with addr_expr
	in the first operand of each pointer_plus.

gcc/testsuite/ChangeLog:

	PR tree-optimization/63184
	* c-c++-common/pr19807-2.c: Enable for all targets and remove the xfail.
	* c-c++-common/pr19807-3.c: Likewise.