Allow %0s $display format specifier

frontends/ast/simplify.cc

@@ -89,7 +89,7 @@ std::string AstNode::process_format_str(const std::string &sformat, int next_arg
 				case 'S':
 				case 'd':
 				case 'D':
-					if (got_len)
+					if (got_len && len_value != 0)
 						goto unsupported_format;
 					YS_FALLTHROUGH
 				case 'x':

tests/simple/string_format.v

@@ -0,0 +1,7 @@
+module top;
+	parameter STR = "something interesting";
+	initial begin
+		$display("A: %s", STR);
+		$display("B: %0s", STR);
+	end
+endmodule