testsuite: Add C++ testcase for PR 126296: `<=>` folding into `<>`.

This adds 2 testcases for fp: `(i <=> j > 0) | (i <=> j < 0)`.
The trapping version was fixed by r17-2709-gde8be0eb05d951
while the non-trapping version was fixed earlier by
r17-2129-gea8c74c074925b.
Since we didn't have a testcase for these cases before,
it would be a good idea to have them.

Pushed as obvious after testing to make sure they work on x86_64-linux-gnu.

	PR tree-optimization/126296

gcc/testsuite/ChangeLog:

	* g++.dg/tree-ssa/pr126296-1.C: New test.
	* g++.dg/tree-ssa/pr126296-2.C: New test.

Signed-off-by: Andrea Pinski <andrew.pinski@oss.qualcomm.com>