clang-format: precedence-based indentation when breaking before operators.

Before:
  bool value = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
               + aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
               + aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
               == aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
                  * bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
                  + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
               && aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
                  * aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
                  > ccccccccccccccccccccccccccccccccccccccccc;

After:
  bool value = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
                       + aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
                       + aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
                   == aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
                              * bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
                          + bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
               && aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
                          * aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
                      > ccccccccccccccccccccccccccccccccccccccccc;

Not particularly pretty, but can probably help to uncover bugs. And if this
bugs somebody, parentheses can help.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@223111 91177308-0d34-0410-b5e6-96231b3b80d8