analyzer: fix ICE in __builtin_isnan (PR 93356)

analyzer: fix ICE in __builtin_isnan (PR 93356)

PR analyzer/93356 reports an ICE handling __builtin_isnan due to a
failing assertion:
  674     gcc_assert (lhs_ec_id != rhs_ec_id);
with op=UNORDERED_EXPR.
when attempting to add an UNORDERED_EXPR constraint.

This is an overzealous assertion, but underlying it are various forms of
sloppiness regarding NaN within the analyzer:

  (a) the assumption in the constraint_manager that equivalence classes
  are reflexive (X == X), which isn't the case for NaN.

  (b) Hardcoding the "honor_nans" param to false when calling
  invert_tree_comparison throughout the analyzer.

  (c) Ignoring ORDERED_EXPR, UNORDERED_EXPR, and the UN-prefixed
  comparison codes.

I wrote a patch for this which tracks the NaN-ness of floating-point
values and uses this to address all of the above.

However, to minimize changes in gcc 10 stage 4, here's a simpler patch
which rejects attempts to query or add constraints on floating-point
values, instead treating any floating-point comparison as "unknown", and
silently dropping the constraints at edges.

gcc/analyzer/ChangeLog:
	PR analyzer/93356
	* region-model.cc (region_model::eval_condition): In both
	overloads, bail out immediately on floating-point types.
	(region_model::eval_condition_without_cm): Likewise.
	(region_model::add_constraint): Likewise.

gcc/testsuite/ChangeLog:
	PR analyzer/93356
	* gcc.dg/analyzer/conditionals-notrans.c (test_float_selfcmp):
	Add.
	* gcc.dg/analyzer/conditionals-trans.c: Mark floating point
	comparison test as failing.
	(test_float_selfcmp): Add.
	* gcc.dg/analyzer/data-model-1.c: Mark floating point comparison
	tests as failing.
	* gcc.dg/analyzer/torture/pr93356.c: New test.

gcc/ChangeLog:
	PR analyzer/93356
	* doc/analyzer.texi (Limitations): Note that constraints on
	floating-point values are currently ignored.