wp_check_php_mysql_versions() outputs messages with no charset defined

[rodrigosprimo]

After [21715] the function wp_check_php_mysql_versions() doesn't define a charset before sending messages to the browser leading to strings with invalid characters in some languages. For example, in Brazilian Portuguese, if the MySQL extension for PHP is not installed the user sees the string below:

Parece que em sua instalação do PHP está faltando a extensão MySQL, que é requesitada pelo WordPress.

I'm not sure if we should simply set the charset calling the header() function (patch attached) or if we should move wp_die() function to another or a new file where it can be used by wp_check_php_mysql_versions() as Nacin proposed in comment:6:ticket:21316. I don't know WP enough to decide where could be a better location for wp_die().

[SergeyBiryukov]

I'm not sure if we should simply set the charset calling the header() function (patch attached)

That's what _default_wp_die_handler() does, so 26536.patch​ looks good to me.

Should probably add a ! headers_sent() check just in case.

[rodrigosprimo]

Add ! hearders_sent() check

[rodrigosprimo]

Should probably add a ! headers_sent() check just in case.

Done, thanks for your feedback.

[nacin]

In 27557:

Send a charset header when erroring out in wp_check_php_mysql_versions().

props rodrigosprimo.
fixes #26536.