Port skipif.inc files to EXTENSIONS

Skip float truncation test under libmysql

We don't return native types for libmysql, so this test doesn't
make sense.

Merge branch 'PHP-7.4'

* PHP-7.4:
Fix #79596: MySQL FLOAT truncates to int some locales

Fix #79596: MySQL FLOAT truncates to int some locales

We must not do locale aware float to string conversion here; instead
we using our `snprintf()` implementation with the `F` specifier.