clang-format: Add option to suppress operator alignment.

With alignment:
  int aaaaaa = aa
               + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
                     * cccccccccccccccccccccccccccccccc;

Without alignment:
  int aaaaaa = aa
      + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
          * cccccccccccccccccccccccccccccccc;

This fixes llvm.org/PR21666.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@223117 91177308-0d34-0410-b5e6-96231b3b80d8