middle-end/96369 - fix missed short-circuiting during range folding

middle-end/96369 - fix missed short-circuiting during range folding

This makes the special case of constant evaluated LHS for a
short-circuiting or/and explicit rather than doing range
merging and eventually exposing a side-effect that shouldn't be
evaluated.

2020-07-31  Richard Biener  <rguenther@suse.de>

	PR middle-end/96369
	* fold-const.c (fold_range_test): Special-case constant
	LHS for short-circuiting operations.

	* c-c++-common/pr96369.c: New testcase.

(cherry picked from commit 505767905735a3c8f171c140108ee263f9fdcad6)