Use php_log_err() rather than _php_error_log_ex()

[Girgias]

Description

I changed the signature of _php_error_log() and removed _php_error_log_ex() on php-src@master and thinking of fully removing the exposed API as I can only find one other usage of it outside of dd-trace which is also always calling _php_error_log() with the same mode.

So rather than doing effectively a function indirection call php_log_err() directly (this is a compat macro on master, but my understanding is you support PHP 7.0 still)

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[realFlowControl]

Thanks @Girgias ❤️
I've triggered our internal GitLab CI job on this PR and will merge once that's green.

[bwoebi]

Hey @Girgias,
This will break on PHP 5 and PHP 7.0. On PHP 7.1+ this is a macro which decays to php_log_err_with_severity, a symbol which did not exist before PHP 7.1.

The problem is that this is a version agnostic zend_extension which we build once - and reuse across all versions (as you can see, it has version checks - and then loads the appropriate ddtrace.so).
(Also, we don't support PHP 5 for ddtrace, but this particular extension is injected regardless of the PHP version, so it just does nothing, but that still requires all symbols to exist.)

If this symbol gets removed on master, the proper fix is using dlsym stuff with disambiguation depending on version number.