* expr.c (safe_from_p): Change code to ERROR_MARK only when not
	accessing nodes.
	* toplev.c (display_help): Add braces to shut up warnings.
	* fold-const.c (non_lvalue): Don't deal with null pointer
	constants here.
	(fold, case COMPOUND_EXPR): Wrap a constant 0 in a NOP_EXPR.

From-SVN: r21698