From Vassil Vassilev:

Enable incremental parsing by the Preprocessor,
where more code can be provided after an EOF.
It mainly prevents the tearing down of the topmost lexer.
To be used like this:
PP.enableIncrementalProcessing();
while (getMoreSource()) {
  while (Parser.ParseTopLevelDecl(ADecl)) {...}
}
PP.enableIncrementalProcessing(false);

llvm-svn: 152914