real: Fix roundeven on inf/nan [PR93663]

real: Fix roundeven on inf/nan [PR93663]

As can be seen in the testcase, roundeven with inf or nan arguments
ICE because of those asserts where nothing prevents from is_halfway_below
being called with those arguments.

The following patch fixes that by just returning false for rvc_inf/rvc_nan
like it returns for rvc_zero, so that we handle roundeven with all those
values as round.  Inf/NaN are not halfway in between two integers...

2020-02-12  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/93663
	* real.c (is_even): Make static.  Function comment fix.
	(is_halfway_below): Make static, don't assert R is not inf/nan,
	instead return false for those.  Small formatting fixes.

	* gcc.dg/torture/builtin-round-roundeven.c (main): Add tests
	for DBL_MAX, inf, their negations and nan.