Add read_at/write_at to missing platforms

core/os/errors.odin

@@ -156,4 +156,12 @@ _error_string :: proc "contextless" (e: Platform_Error) -> string where intrinsi
 		return ti.names[idx]
 	}
 	return "<unknown platform error>"
-}
+}
+
+@(private, require_results)
+error_to_io_error :: proc(ferr: Error) -> io.Error {
+	if ferr == nil {
+		return .None
+	}
+	return ferr.(io.Error) or_else .Unknown
+}