Fixed handling of comments before preprocessor directives.

Comments before preprocessor directives used to be stored with InPPDirective
flag set, which prevented correct comment splitting in this case. Fixed by
flushing comments before switching on InPPDirective. Added a new test and fixed
one of the existing tests.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178261 91177308-0d34-0410-b5e6-96231b3b80d8