* fold-const.c (fold_convert): Rename to fold_convert_const.
	(fold_convert_const): Change arguments to take a tree_code,
	a type and the operand/expression to be converted.  Return
	NULL_TREE if no simplification is possible.  Add support for
	FIX_CEIL_EXPR and FIX_FLOOR_EXPR in addition to FIX_TRUNC_EXPR.
	(fold): Handle FIX_CEIL_EXPR and FIX_FLOOR_EXPR.
	Adjust call to fold_convert to match new fold_convert_const.
	Avoid modifying the tree passed to fold in-place.

From-SVN: r76237