analyzer: handle comparisons against negated symbolic values [PR107948]

analyzer: handle comparisons against negated symbolic values [PR107948]

gcc/analyzer/ChangeLog:
	PR analyzer/107948
	* region-model-manager.cc
	(region_model_manager::maybe_fold_binop): Fold (0 - VAL) to -VAL.
	* region-model.cc (region_model::eval_condition): Handle e.g.
	"-X <= 0" as equivalent to X >= 0".

gcc/testsuite/ChangeLog:
	PR analyzer/107948
	* gcc.dg/analyzer/feasibility-pr107948.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>