[msan] Fix origin tracking in unaligned load/store.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@195130 91177308-0d34-0410-b5e6-96231b3b80d8
[asan] remove a fixed FIXME; extend the comment around __sanitizer_annotate_contiguous_container

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@195131 91177308-0d34-0410-b5e6-96231b3b80d8