Fix ASan init function detection after clang r208128.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208141 91177308-0d34-0410-b5e6-96231b3b80d8
[Support/MemoryBuffer] Remove the assertion that the file size did not shrink.

This can happen in practice with the user changing files and we can recover from it.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208143 91177308-0d34-0410-b5e6-96231b3b80d8