clang-format: Fix parsing of conditional expressions.

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

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

llvm-svn: 213258