clang-format: Improve constructor initializer linewrapping.

Specifically make ConstructorInitializerAllOnOneLineOrOnePerLine work
nicely with BreakConstructorInitializersBeforeComma.

This fixes llvm.org/PR17395.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@192168 91177308-0d34-0410-b5e6-96231b3b80d8