[asan] introduce __asan_load_cxx_array_cookie: check that the array cookie...

[asan] introduce __asan_load_cxx_array_cookie: check that the array cookie address is properly poisoned and return the cookie value. If not, return 0 to avoid infinite loop of DTORs (in case of use-after-free). Calls to this function will be inserted by clang (separate change)

llvm-svn: 216692