Adds the -vfsoverlay frontend option that enables the user to pass
VFS overlay YAML files to Swift. These files define a (potentially
many-layered) virtual mapping on which we predicate a VFS.
Switch all input-based memory buffer reads in the Frontend to the new
FileSystem-based approach.
- Added missing ifdef guard in PointerIntEnum header
- Consistent naming convention for ifdef guards
- Consistent 'end namespace swift'
- Consistent single EOL at end of header files
Equivalent to llvm::sys::fs::rename, except that if the destination file
exists and has the same contents as the source file, the source file is
simply deleted and the destination file is not touched.
Used in next commit.
Swift SVN r28041
