Allow sanitizer to work with "old" kernel headers

Sanitizers work on ancient kernels and were depending on types existing.
When those types were removed, the sanitizer build broke. See bug
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59009 for more information.

This patch fixes it by isolating the need for those types only when the
feature is actually needed, thus allowing one to compile the kernel with
or without that change, irrespective of its version.

Patch by Christophe Lyon.

llvm-svn: 230324