We need to install a number of additional packages that are installed
by default on the AMD64 workers.

We also have to manually set up the MySQL user.

For now we don't set up Postgres -- if anyone wants to figure that
out, it would be great ;)

Log redirections in compile.sh are removed, because /dev/stdout is
not accessible. We don't see to use this anyway.

Reduce duplication.

This adds the Autoconf's --enable-option-checking=fatal option so
when non existing option from the PHP's configure options is used
a fatal error happens.

Add --enable-werror configure option and use it on Travis. It's not
possible to directly use CFLAGS, because it also affects configure
checks which often throw warnings.

We can't enable something similar for Windows builds at this time,
because they throw a lot more warnings.

Compile the zend_test extension as shared and try loading it with dl()
to test for obvious issues. Doing this as a standalone call because this
is very specific to the CI setup.