Cut off parsing early during code completion

These calls to ConsumeCodeCompletionToken() caused parsing to continue
needlessly when an immediate cutOffParsing() would do.

Document the function to clarify its correct usage.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@207823 91177308-0d34-0410-b5e6-96231b3b80d8
Remove unused IncrProcessing parameter from Preprocessor ctor

Preprocessor::enableIncrementalProcessing() provides a consistent interface to
enable the feature.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@207824 91177308-0d34-0410-b5e6-96231b3b80d8
Factor TargetInfo pointer/DelayInitialization bool pair out of Preprocessor ctor

The Preprocessor::Initialize() function already offers a clear interface to
achieve this, further reducing the confusing number of states a newly
constructed preprocessor can have.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@207825 91177308-0d34-0410-b5e6-96231b3b80d8
Reformat code following Preprocessor constructor updates

Landing this separately to make the previous commits easy to follow at home.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@207826 91177308-0d34-0410-b5e6-96231b3b80d8