This fixes printing a REAL_CST generated from value-numbering
punning some bits to a real which turns out as zero with big
negative exponent.  This causes the loop in real_to_decimal_for_mode to
never terminate.

2020-05-14  Richard Biener  <rguenther@suse.de>

	PR middle-end/95118
	* real.c (real_to_decimal_for_mode): Make sure we handle
	a zero with nonzero exponent.

	* gcc.dg/pr95118.c: New testcase.