skins2(Linux): replace tempnam() with mkdtemp()
skins2(Linux): replace tempnam() with mkdtemp()

Linux manual strongly advises against using tempnam().

(cherry picked from commit 27cb7a2eddae5bd4e730ca7fff5b05cffd1b691c)
Signed-off-by: Erwan Tulou <e27b355b6a481153648f03262de342e9eb9e2807@videolan.org>

jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2