Change MemoryBuffer::getFile to take a Twine.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193429 91177308-0d34-0410-b5e6-96231b3b80d8
Try to fix the build on windows.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193431 91177308-0d34-0410-b5e6-96231b3b80d8