builtin,cgen: rename Option to _option (#14317)

vlib/builtin/option.v

@@ -121,6 +121,23 @@ fn opt_ok(data voidptr, mut option Option, size int) {
 	}
 }
 
+// option is the base of V's internal optional return system.
+struct _option {
+	state u8
+	err   IError = none__
+	// Data is trailing after err
+	// and is not included in here but in the
+	// derived _option_xxx types
+}
+
+fn opt_ok2(data voidptr, mut option _option, size int) {
+	unsafe {
+		*option = _option{}
+		// use err to get the end of OptionBase and then memcpy into it
+		vmemcpy(&u8(&option.err) + sizeof(IError), data, size)
+	}
+}
+
 struct _result {
 	is_error bool
 	err      IError = none__