Enable building ART with clang

Change-Id: I36bf66a90dfc03d27e2888d24d074a37fdac67d3

Fix compile error and silence the chatty ART if it is built with clang

Change-Id: Ia23c95fc56d0334622f0ff1e59ed7d579af16211
Don't rely on GCC extensions. Credit to Bernhard Rosenkränzer, I just had to rework this for the kitkat branch.
Derp.
Fix build.
Reduce logging verbosity by default to ERROR

This is probably not the best way to disable logging spam. It'll be changed if there is a better solution.

Change-Id: Ie4af4a8897c109c364ea65745c55105c6d88485b