Description:
------------
BCMath reports some errors and warnings (such as "exponent too
large in raise") by directly writing to stderr[1], thereby
completely bypassing PHP's error handling.

[1] <https://github.com/php/php-src/blob/php-7.0.23/ext/bcmath/libbcmath/src/rt.c>


Test script:
---------------
<?php

set_error_handler(function ($errno, $errstr) {
    var_dump('caught');
});
bcdiv('1', '0');
bcpow('1', '12345678901234567890');


Expected result:
----------------
string(6) "caught"
string(6) "caught"


Actual result:
--------------
string(6) "caught"
bc math error: exponent too large in raise