clang-format: Improve formatting of constructor initializers.

Before:
  Constructor()
      : aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(aaaaaaaaaaaaaaaaaaaaaaaaa(aaaa,
                                                                      aaaa)) {}
After:
  Constructor()
      : aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
            aaaaaaaaaaaaaaaaaaaaaaaaa(aaaa, aaaa)) {}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194210 91177308-0d34-0410-b5e6-96231b3b80d8