Some upcoming changes like https://wiki.php.net/rfc/deprecate_null_to_scalar_internal_arg
will make it somewhat inconvenient to determine whether a given
function invocation will generate a diagnostic. Rather than trying
to exclude this in advance, call the function with diagnostics
suppressed, and check whether anything was thrown.
This adds a new EG flag that is kept specific to the SCCP use-case.
This does not use the error_cb hook as it is a (non-TLS) global,
and doesn't fully suppress error handling besides.
Test this by removing the in advance checks for implode and array_flip.
This only moves the files, adjusts the build system, exports APIs
and does minor fixups to make sure the code builds.
This does not yet try to make the optimizer usable independently
of opcache.
Closes GH-6642.