+ * return value is all-ones in this case.
+ *
+ * Test code:
+ * char *endptr;
+ * const char *minus = "-";
+ * errno = 0;
+ * bb_strtoi(minus, &endptr, 0); // must set ERANGE
+ * printf("minus:%p endptr:%p errno:%d EINVAL:%d\n", minus, endptr, errno, EINVAL);
+ * errno = 0;
+ * bb_strtoi("-0-", &endptr, 0); // must set EINVAL and point to second '-'
+ * printf("endptr[0]:%c errno:%d EINVAL:%d\n", endptr[0], errno, EINVAL);