vlc: fix compile error with uClibc-ng Linuxthreads

The fallback code path didn't work correctly, so fix it.

Fixes:
  http://autobuild.buildroot.net/results/3122287ddea1e316a64ccf0d0dc9415bfefebb49/



Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>