Don't use PathV1.h in LTOCodeGenerator.cpp

This patch also adds a simpler version of sys::fs::remove and a tool_output_file
constructor for when we already have an open file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184095 91177308-0d34-0410-b5e6-96231b3b80d8