virmock: Initialize both symbols in VIR_MOCK_REAL_INIT_ALT

virmock: Initialize both symbols in VIR_MOCK_REAL_INIT_ALT

It may happen that both symbols are present. Especially when
chaining mocks. For instance if a test is using virpcimock and
then both stat and __xstat would be present in the address space
as virpcimock implements both. Then, if the test would try to use
say virfilewrapper (which again uses VIR_MOCK_REAL_INIT_ALT() to
init real_stat and real___xstat) it would find stat() from
virpcimock and stop there. The virfilewrapper.c:real___xstat
wouldn't be initialized and thus it may result in a segfault.

The reason for segfault is that sys/stat.h may redefine stat() to
call __xstat().

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>