- Add new TPPClingCallbacks class & two new methods TCling__CompileMacro...

... and TCling__SplitAclicMode

The FileNotFound() method of TPPClingCallbacks is called via
Callbacks->FileNotFound(Filename, RecoveryPath) in
Preprocessor::HandleIncludeDirective(), allowing to compile code via
ACLiC when specifying #include "myfile.C+", and hence suppressing
preprocessor error message like:
input_line_23:1:10: fatal error: 'myfile.C+' file not found