Also, __USE_UNIX98 is a libc-internal definition. The build system is
not supposed to define that directly (we have _GNU_SOURCE).

This fix actually removes traces of the libc _LARGEFILE64_SOURCE
transitional API.
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

Pointed-out-by: Benjamin Gerard

So that the plugins can be installed at the good place

We really want plugins to resolve their VLC symbols against the already
loaded LibVLC core, rather than with their own version of it.
Performance benefit should be neglectible, if any.
Still, this will "fix" the plugin crash with static LibVLC builds (or
generate a due link-time error). Anyway, this is one step toward
supporting any form of static linking again.

(Don't expect this to work yet though)