audit: mark as not available for static builds

audit uses -fPIE/-pie, which is not compatible with static only builds
with uClibc. Since using audit in a statically linked environment is
probably not a very common use case, let's simply mark it as
non-available in such situations.

Fixes:

  http://autobuild.buildroot.net/results/549492270f3f43747a96a8326aef1d7ae1d3b213/



Thanks to Waldemar for explaining the source of the problem.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>