tree-ssa-ccp.c (set_rhs): Change function to return a bool.

tree-ssa-ccp.c (set_rhs): Change function to return a bool.

	* tree-ssa-ccp.c (set_rhs): Change function to return a bool.
	Ensure the replacement rhs is valid gimple before performing
	the substitution.  Return false if these sanity checks fail.
	(fold_stmt): Only set changed to true, if set_rhs returns true.
	(execute_fold_all_builtins): Only call modify_stmt if set_rhs
	succeeds.

From-SVN: r84091