Hi all,

This tiny patch adds support for KernelASan. KASan brings Asan error 
detection capabilities to Linux kernel 
(https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel).

KASan works similar to normal userspace ASan but disables some options 
which are not yet supported by kernel (notably inline instrumentation, 
stack/global protection and UAR). We would prefer to hide all necessary 
tweaks under a user-friendly flag (-fsanitize=kernel-address) instead of 
forcing them directly in kernel's CFLAGS.

Kernel patches are currently under review in LKML 
(https://lkml.org/lkml/2014/7/9/990).

Bootstrapped and regtested on x64.

Ok to commit?

-Y