Handle location wrappers better in warn_logical_operator.

Handle location wrappers better in warn_logical_operator.

When we introduced location wrappers, we added fold_for_warn to warnings
that are interested in a constant value, or wrapper-stripping to warnings
that are interested in literal constants.  This particular warning is
looking for a literal constant, but was wrongly changed to use
fold_for_warn; this patch makes it strip instead.

	* c-warn.c (warn_logical_operator): Strip location wrappers.  Don't
	fold_for_warn in "|| mask" warning.

From-SVN: r275743