Ensure the Meson build also supports private memory
Ensure the Meson build also supports private memory

The meson build does not check for `mlock()` and define `HAVE_MLOCK`.

Fixes https://gitlab.gnome.org/GNOME/libsecret/issues/23

GNOME/libsecret,GNOME/libsecret,GNOME/libsecret,GNOME/libsecret