Add a unit test for checking that we respect the F_Binary flag.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186676 91177308-0d34-0410-b5e6-96231b3b80d8
Split openFileForWrite into windows and unix versions.

It is similar to 186511, but for creating files for writing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186679 91177308-0d34-0410-b5e6-96231b3b80d8