[clang-format] Separate line comment sections after a right brace from comment...

[clang-format] Separate line comment sections after a right brace from comment sections in the scope.

Summary:
The following two comment lines form a single comment section:
```
if (1) { // line 1
   // line 2
}
```
This is because the break of a comment section was based on the original column
of the first token of the previous line (in this case, the 'if').
This patch splits these two comment lines into different sections by taking into
account the original column of the right brace preceding the first line comment
where applicable.

Reviewers: djasper

Reviewed By: djasper

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D29291

llvm-svn: 293539