[ASan] When iterating over segments on OSX, treat the segments' initial
protection level as their current protection level.
This fixes the UNIMPLEMENTED check that started to fire on OSX after r210649.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@211713 91177308-0d34-0410-b5e6-96231b3b80d8