Modules and Tooling tests in particular tend to want to change the cwd,
so we were missing test coverage in this area on Windows. It should now
be easier to write such portable tests.
llvm-svn: 231029
With modules we start accessing headers for the first time while reading
the module map, which often has very different paths from the include
scanning logic.
Using the name by which the file was accessed gets us one step closer to
the right solution, which is using a FileName abstraction that decouples
the name by which a file was accessed from the FileEntry.
llvm-svn: 215541