re PR middle-end/49705 (-Wstrict-overflow should not diagnose unevaluated expressions)

gcc/c-family:
	PR middle-end/49705
	* c-common.c (c_disable_warnings): New static function.
	(c_enable_warnings): New static function.
	(c_fully_fold_internal): Change local unused_p to bool.  Call
	c_disable_warnings and c_enable_warnings rather than change
	c_inhibit_evaluation_warnings.
gcc/testsuite:
	PR middle-end/49705
	* gcc.dg/pr49705.c: New test.

From-SVN: r176591