[asan] Fix malloc interception on Android L Preview.

Format of __libc_malloc_dispatch has changed in Android L.
While we are moving towards a solution that does not depend on bionic
internals, here is something to support both K* and L releases.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@213263 91177308-0d34-0410-b5e6-96231b3b80d8