[asan] Relax the null_deref.cc test even further

On Darwin/x86_64, asan may report the crashing line of NullDeref as line
19 (i.e the closing brace of the function), whereas on other targets we
see line 15 ("ptr[10]++").

The optimized debug info here isn't reliable enough to check.

rdar://problem/41526369

llvm-svn: 335747