the atomic writes option, since the intent is that this option be set for an
entire build, which may have any number of compiler instances writing to the
same output file.
llvm-svn: 124772
callbacks class.
- Aside from being generally cleaner, this also allows -H to work correctly in
modes other than standard preprocessing (e.g., -c, -MM, etc.)
llvm-svn: 124723
