clang-format: Fix parsing of conditional expressions.

Before:
  aaaaaa = aaaaaaaaaaaa ? aaaaaaaaaa ? aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
      : aaaaaaaaaaaaaaaaaaaaaa
      : aaaaaaaaaaaaaaaaaaaaaaaaaaaa;

After:
  aaaaaa = aaaaaaaaaaaa
               ? aaaaaaaaaa ? aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
                            : aaaaaaaaaaaaaaaaaaaaaa
               : aaaaaaaaaaaaaaaaaaaaaaaaaaaa;

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@213258 91177308-0d34-0410-b5e6-96231b3b80d8