PR sanitizer/67258
	* ubsan/ubsan_type_hash.cc: Cherry pick upstream r244101.

Upstraem patch:
commit 1d2477faafda9ad2cc19927b3c31efd22747f013
Author: Alexey Samsonov <vonosmas@gmail.com>
Date:   Wed Aug 5 19:35:46 2015 +0000

    [UBSan] Fix UBSan-vptr false positive.

    Offset from vptr to the start of most-derived object can actually
    be positive in some virtual base class vtables.

    Patch by Stephan Bergmann!

    git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@244101 91177308-0d34-0410-b5e6-96231b3b80d8

From-SVN: r227591