Fix non posix test construction in configure.

POSIX does not document the == construction for test; Even if GNU test and bash builtin allow it, configure is run by sh and FreeBSD test does not allow it so that this test is always false there.
Signed-off-by: Christophe Mutricy <xtophe@videolan.org>

configure.ac

@@ -1572,7 +1572,7 @@ dnl Allow runing as root (usefull for people runing on embedded platforms)
 dnl
 AC_ARG_ENABLE(run-as-root,
 [  --enable-run-as-root    allow runing VLC as root (default disabled)])
-AS_IF([test "${enable_run_as_root}" == "yes"],[
+AS_IF([test "${enable_run_as_root}" = "yes"],[
     AC_DEFINE(ALLOW_RUN_AS_ROOT, 1,
               [Define to 1 to allow runing VLC as root (uid 0).])
 ])