This avoids a fatal error on PHP 8 if `error_reporting()` is disabled in `php.ini`.
On systems with this function disabled, it's best to add a dummy function to the `wp-config.php` file, as there are multiple other calls in core or plugins.
However, as this call to the function is run prior to `wp-config.php` loading, it is now wrapped in a `function_exists()` check.
Follow-up to [50447].
Props gansbrest, sabernhardt, jrf, martin.krcho, SergeyBiryukov.
Fixes#61873.
Built from https://develop.svn.wordpress.org/trunk@58905
git-svn-id: http://core.svn.wordpress.org/trunk@58301 1a063a9b-81f0-0310-95a4-ce76da25c4cd
8efc6e1807