[clang-format] Fix shortening blocks in macros causing merged next line

Summary:
This patch addresses bug 36002, where a combination of options causes the line
following a short block in macro to be merged with that macro.

Reviewers: bkramer

Reviewed By: bkramer

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D42298

llvm-svn: 322954