Put short if statements on a single line.

Before: if (a)
          return;
After:  if (a) return;

Not yet sure, whether this is always desired, but we can add options and
make this a style parameter as we go along.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172413 91177308-0d34-0410-b5e6-96231b3b80d8