Several improvements to the formatting of static initializers.

1. Never avoid bin packing in static initializers as this can
   lead to terrible results.
2. If an element has to be broken over multiple lines, break after
   the following comma.

This should be a step forward, but there are still many cases
especially with nested static initializers that we handle badly.
More patches will follow.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174061 91177308-0d34-0410-b5e6-96231b3b80d8