Check rvc_normal in real_isdenormal.

Check rvc_normal in real_isdenormal.

[-Inf, -Inf] is being flushed to [-Inf, -0.0] because real_isdenormal
is being overly pessimistic.  It is missing a check for rvc_normal.
This doesn't cause problems in real.cc because all uses of
real_isdenormal are already on the rvc_normal path.  The uses in
value-range.cc however, are not.

This patch adds a check for rvc_normal.

gcc/ChangeLog:

	* real.h (real_isdenormal): Check rvc_normal.
	* value-range.cc (range_tests_floats): New test.